and the frontier of Sikkim. The better class of teas cost at Lhassa about two rupees per pound, but are seldom imported. It is estimated that the annual supply of tea to Thibet amounts to about six millions of pounds, producing an income of not less than 300,000!. A NEW Source of caoutchouc reaches us from Burmah, a description of which has been given in a pamphlet published in Rangoon. The plant yielding this caoutchouc is the Chavannesia esculenta, a creeper belonging to the natural order Apocyneæ, an order which includes the Borneo rubber plant Urceola clastica, the African rubber plants Landolphia spp., as well as other genera yielding milky juices. The plant, which is common in the Burmese forests, is said to be cultivated by the natives for the sake of its fruit, which has an agreeable acid taste. comes into season when tamarinds are not procurable, and finds a ready sale at Rangoon, at an anna per bunch of ten fruits. The milk is said to coagulate more readily than that of Ficus elastica, and to be purer and better for most purposes for which rubler is used. It UNDER the title of "Contributions to the Fossil Flora of the Western Territories, U.S., Part I. The Cretaceous Flora, by Prof. Lesquereux," Prof. Hayden has published the sixth volume of the series of final reports of the United States Geological Survey of the Territories. The work is in quarto, and embraces 136 pages an 1 thirty plates. Very many new species are figured and described. The work covers all the known species of the Dakota group, and constitutes an important starting-point for similar monographs of other divisions of the fossil plants of America. Prof. Lesquereux considers the surface and stratigraphical distribution of the species. In accordance with Dr. Hayden's views, the author finds the group to be of marine origin, as shown by the occurrence of various species of marine molluscs. Prof. Lesquereux is not prepared to commit himself in regard to the correlaton of the flora of the Dakota group with that of subsequent geological epochs and their identity, preferring to wait the gathering and examination of other series. He, however, states that this flora, without affinity with any preceding vegetable types, without relation to the flora of the Lower Tertiary of the United States, and with scarcely any forms referable to species known from coeval formations in Europe, presents, as a whole, a remarkable and, as yet, unexplained case oli olation. THE cultivation of the tobacco plant in Algeria has been carried out very successfully, the soil and climate of that country being well suited to the growth of the plant. In 1874 no less than 4,850,00 kilogrammes, or over 9,700,000 lbs., were produced and passed thro ugh the State warehouses. The value of this crop was 141, 2247., or nearly double that of 1873. The experiment-though it is no longer merely an experiment, but a practical industry-has been carried on since 1847, and during the past twenty-seven years about 140,000,000 lbs. weight of tobacco has been produced and sold. Ir is stated that the Italian Government, following the course it has already adopted on previous occasions, will gratuitously distribute this year 5,000 plants of the Eucalyptus globulus, for cultivation in the Agro Romano, especially in the spot infected by malaria. THE additions to the Zoological Society's Gardens during the past week include an African Civet Cat (Viverra civetta), presented by the Earl of Harrington; an Australian Monitor (Monitor gouldi), presented by Dr. Pardoe; three Black-necked Storks (Xenorhynchus australis) from Malacca, purchased; a Blue-faced Green Amazon (Chrysotis bouqueti) from St. Lucia; two Yellow-fronted Amazons (Chrysotis ochrocephala) and a Brown-throated Conure (Conurus æruginosus) from S. America, deposited. ACCIDENTAL EXPLOSIONS * THE term "accident," applied in its strict sense to disasters caused by explosions, would imply that these were due to some circumstance, or combination of circumstances, entirely unforeseen, and that they were consequently unpreventible. An explosion which occurs during the preparation or investigation of a compound the explosive nature of which is as yet unknown may be purely accidental, but if, after the properties of the sab stance have been thoroughly ascertained and made known, an explosion occurs during its production, by some person who has not properly made himself acquainted with or has neglected in some point or other those conditions essential to its production with safety, the knowledge of which is within his reach, the term "accidental" can certainly not be properly applied to it, although in all probability it would be so designated popularly, and even by those entrusted on behalf of the public with the investigation of its origin and results. In the present discourse the definition "accidental" is accepted in the loose sense in which it is popularly applied to explosions, with the object of examining into the nature and causes of such explosions, and, if possible, of indicating direc tions in which there may be hope of successful efforts being made for reducing the frequency of their occurrence. The phenomena attendant upon an explosion are generally due to the sudden or very rapid expansion of matter, accom panied in most instances by its change of state from solid or liquid to gas or vapour. The most simple classes of explosions are those caused by the sudden yielding to force, exerted from within, of receptacles in which a gas is imprisoned in a highly compressed condition, or a liquid has been raised to a temperature greatly exceeding that at which its molecules have a tendency to fly asunder or to assume the state of vapour or gas. The strength or elasticity of the envelope which confines them suddenly yielding to pressure, the liquid passes with great rapidity into vapour, violently displacing by this sudden expansion the sur rounding air and any other obstacles opposed to the expanding molecules. Similar explosive effects less simple in their origin are brought about by the sudden development of chemical activity in mistures of gases or vapours, of solids and gases, or of solids only. or in chemical compounds of unstable character, the result in all such instances being the development of intense heat and the sudden or very rapid and great expansion of matter. Examples of the most simple class of explosions are the sudden failure in strength at some particular point, or generally, of the material composing a vessel in which a gas has either been liqe fied or highly compressed. Accidental explosions of this cha racter take place chiefly, and happily not very frequently, in the laboratory or lecture room, yet instances occasionally occur of disastrous explosions resulting from such causes in manufacturing operations, or in the practical application of compressed air cr other gases. The most recent illustration of a serious accidental explosion of this kind is that which occurred in the Arsenal a Woolwich in January 1874, with the air-chamber of a White head, or Fish torpedo, when one man lost his life and severa were seriously injured. In this instance some part of the sof steel diaphragm closing the chamber in which the motive power of this self-propellant torpedo (air) was imprisoned under a pressure of about 800 lb. on the square inch, suddenly yielded to the efforts of the gas to return to its normal condition. Other explosions of this class, which are of more than weekly occurrence, and but too frequently result not merely in destro tion of property, but in more or less serious loss of life, are cat to the bursting of boilers at factories, mines, and collieries, 1 say nothing of those which occur in buildings, in connection with heating appliances and with kitchen ranges, and bathr other heating-arrangements. The explosion of a boiler ! arise either from an exceptionally rapid development of sa or from an absence, or failure in the proper operation, of appa ances for relieving the pressure in a boiler, by permitting the escape of steam and giving warning when the pressure beg exceed that of safety. But by far the chief causes of explosions are defects in their construction or repair, and the reduction in thickness of the metal in parts by corrosion of oxidation, internally and externally, from long use, and sege of proper measures for periodically cleaning the boilers The accidents due directly to the deposits formed from water in boilers have been very greatly diminished of late years by the *Abstract of a lecture delivered at the Royal Institution, March 14 by Prof. F. A. Abel, F.R.S. used. application of preparations called boiler-compositions, of which there are many varieties, their general action being to prevent more or less effectually the carbonate and sulphate of calcium and other impurities in water, which are separated by its ebullition and evaporation, from producing hard impenetrable crusts or coatings upon the inner surfaces of the boiler. The judicious employment of a good anti-fouling preparation, and the thorough periodical cleansing of the interior of boilers, go far to guard against that source of danger; though, in adopting measures to diminish the formation of incrustations, care must also be taken to avoid promoting internal corrosion of the boiler by the agents The operations of the Manchester Steam Users Association for the prevention of steam-boiler explosions, founded, mainly through the instrumentality of Sir William Fairbairn, twenty years ago, and of which Sir Joseph Whitworth has also been a warm supporter from its commencement, appear to have gradually succeeded in very importantly reducing the annual number of boiler explosions by introducing among its members a system of periodical independent inspection. The Association will not allow that the term "accidental," or mysterious, is applicable to steam boiler explosions. Mysterious they certainly are not, as they are generally quite traceable to causes which may be obviated, such as inferior material or defective construction, or local injuries, gradually developing and increasing, which would certainly be discovered before they attained dangerous dimensions, by a proper inspection. The following data with respect to the causes of boiler explosions are taken from a table prepared by Mr. L. Fletcher, chief engineer of the Association:-40 per cent. were due (from Jan. 1861 to June 1870) to malconstruction of the boilers; 29 per cent. to "defective condition" of the boilers; 15 per cent. to the failure of seams of rivets at the bottom of externally fired boilers; 10 per cent. to overheating from shortness of water; and less than 3 per cent. to accumulation of incrustations. An examination into the particular nature of the services performed by boilers which have exploded shows that a considerable number of explosions have cccurred at ironworks, and a very large proportion at collieries, where plain cylindrical externallyfired boilers are much used. Many of the explosions of these particular boilers arise from places which remain for a time concealed in the overlaps of the seams of rivets, defying detection, but gradually extending from one rivet hole to another, till some udden strain causes them to extend throughout the entire seam, the boiler splitting in two. The particular description of boiler which gave rise to the largest number of fatal accidents during the year taken as illustration was the single-flued or Cornish boiler; and it was stated by Mr. Fletcher that all these explosions must have been the result of glaring neglect, as there is no boiler safer to use when well made and properly cared for. The simple precaution of strengthening or giving internal support to the sides of the furnace-tube of these boilers, the importance of which was demonstrated many years ago by Sir W. Fairbairn, appears to be still greatly neglected, the result being the frequent collapse of the tube through weakness. Very few explosions in 1873 appear to have been due to the neglect of the attendants, but by far the greater number to that of the boiler owners or the makers. [The lecturer then gave a number of instances strikingly illustrative of the statements above made.] The foregoing and other very numerous illustrations of the appalling display of ignorance, neglect, or recklessness in dealing with the application of steam power, point strongly to the importance of legislation connected with this subject. There can be no reason why the responsibility of the proper condition of boilers and steam apparatus generally should not be thrown upon inspectors, just as the proper fencing of machinery in factories, and the proper condition of steam boilers in a passenger steamship, are secured by a system of responsible official inspection. The explosions which are often recorded as occurring in kitchen ranges and in boilers used in connection with the heating of buildings are not unfrequently attended by fatal results. Much of what has been said with regard to boiler explosions generally applies to accidents of this class. As the water in kitchen boilers is often used for culinary and drinking purposes, the means employed in boilers used for steam purposes only, to prevent the formation of hard deposits, cannot be resorted to; therefore the only means of guarding against accidents to domestic boilers from these causes consists in frequent and thorough cleaning out, which is especially neces sary where the water supply is hard. Explosions also cccur with household boilers of the ordinary circulating class, unprovided with safety valves, through the stoptaps of the pipes which connect them with an overhead cistern being left closed by accident or negligence, in which case steam pressure must speedily accumulate to a dangerous extent, all outlets being closed. Accidents with such boilers are particularly liable to occur during severe frosts in consequence of the circulating pipes becoming plugged up with ice, whereby the outlet for steam pressure is as completely cut off as if the stoptaps were closed. Several accidents due to these two causes, some of them attended by fatal results, were recorded last year. The obvious and simple method of guarding effectually against such explosions is to have the boiler fitted with a reliable safety valve, of the most simple form. Explosions resulting from the ignition of mixtures of inflammable gas and air constitute even a more formidable class than that just described, for the number of explosions in coal mines which occur in a year is very considerably greater than that of boiler explosions, while the loss of life occasioned by the former is very considerable, and is occasionally appalling in its magnitude. If marsh-gas, or light carburetted hydrogen, which exists imprisoned in coal-beds and escapes into the atmosphere in the pit-working, either gradually or sometimes under considerable pressure, becomes mixed with the air to such an extent that there are about eighteen volumes of the latter to one of the gas, the mixture burns with a pale blue flame, which will surround that of a candle contained in such an atmosphere; the appearance of such a "corpse light" round the flame of the pitman's candle or lamp-flame is a warning, too generally unheeded, of the presence of fire-damp in quantities likely to be dangerous, for if the proportion of marsh gas increases much beyond that above specified, an explosive atmosphere will be formed, the violent character of which increases as the propor tion of fire-damp approaches that of one volume to ten of air. Marsh-gas requires for its ignition to be brought into contact with a body raised to a white heat; fire-damp, cr a mixture of marsh-gas and air is therefore not inflamed by a spark or red-hot wire, but will explode if brought into contact with flame. The fact that this contact must be of some little duration to ensure the ignition of the fire-damp was applied by Stephenson in the construction of his safety-lamp; and a very philosophical application of the property possessed by good conducting bodies, such as copper or iron, of cooling down a flame below the igniting point of the gas, and thus ex inguishing it, was made by Davy in the construct on of his safety-lamp. All the efforts of eminent scientific and practical men, for the better part of a century past, to diminish the number of coal-mine explosions by improving the ventilation of the mines and providing the miner with comparatively safe means of illumination, appear to have had very little effect in reducing the number and disastrous nature of these accidents. Since the construction of safety miners' lamps by Davy, Stephenson, and Clenney, repeated and partially successful efforts have been made to reduce the loss of light consequent upon the necessary enclosure of the flame, and thus to lessen the temptation of the miner to employ a naked flame at his work in fiery mines; yet investigations after mine explosions still frequently disclose instances of the employment of candles where they are undoubtedly dangerous, and the regulations which have been made law with the view of preventing accidents through the use of naked lights by miners, where there appears any likelihood of fire-damp escaping and lodging, are in many cases either habitually neglected or very carelessly carried cut. One practice which appears to have become very general in mines where fire-damp is known to exist, that of sending firemen with safety-lamps to examine the mines, the men then proceeding to work with naked lights in all places marked as safe by those officials, is obviously a most dangerous one, the lives of many being made absolutely dependent upon the vigilance and trustworthiness of one or two; yet it appears to be one almost forced upon the managers of collieries by the men themselves, who often absolutely refuse to go to work with safety-lamps. Of the three colliery accidents which occurred between Dec. 23 and Jan. 7 last, by which twenty-eight men lost their lives, two afford sad illustrations of the fact that the overlookers and the miners themselves are chiefly to blame for the frequency of these accidents, and that the practice of employing "firemen" just referred to is a highly perilous one. There can be no question that the comparatively dim light afforded even by the best constructed lamps in general use is a cause of great temptation to the men to use uncovered lights; it is therefore much to be hoped that continued efforts may be made to apply the electric light to the illumination of mine workings. Some approach to success in this direction was already attained ten years ago, and one cannot but have great faith in the ultimate feasibility of some portable method of illumination by electric agency. There are, however, causes other than the use of unprotected lights, which contribute to the production of coal-mine explosions. Efficient ventilation of workings, whether in use or not, whereby all dangerous accumulation of fire-damp is avoided, and any suiden eruption of gas may be rapidly dealt with (the gas being largely diluted and swept away as speedily as possible), is indispensable to the safe working of the mine (without any reference to the health of the men) so long as there is any temptation for the use of naked lights. The original laying out of a working greatly affects the question of efficient ventilation, and explosions have been clearly traced to gas accumulations, which there was sufficient power of ventilation to reduce, if the nature of the working had admitted of its proper application. In arranging for the efficient ventilation of a mine, ample provision for rapidly applying extra artificial ventilating power should be made, and, in connection with this, the interesting and useful series of observations should be borne in mind which have been made public in communications to the Royal Society and the Meteorological Society by Messrs. R. H. Scott and W. Galloway.* Since the employment of gunpowder as a means of rapidly removing coal, or overlying shale, has come into considerable use, there can be no question that an additional and a very serious source of danger has been imported into the working of collieries. That the explosion of a charge of powder in a blasthole, or the "firing of a shot," has by no means unfrequently resulted in the production of a fire-damp explosion, has been clearly established by careful inquiry. This has been ascribed to two causes, one of them the direct ignition of the explosive gas-mixture by the flame from the shot, the other the dislodgment of fire-damp from cavities or disused workings by the concussion produced, and its ignition by some naked flame or defective lamp in the neighbourhood. If a shot takes effect properly (i.e. if the force is fully expended in breaking the coal or rock at the seat of the charge), there is seldom flame produced, but if the tamping which confines the charge in the blast-hole is simply blown out of the latter like a shot from a gun (which not unfrequently occurs when the rock is very hard or the tamping is not sufficiently firm, or when the charge of powder is excessive), the powder-gas issuing from the blast-hole will produce a flash of fire as obtained with a gun, and if the fire-damp were in the immediate neighbourhood, it would no doubt be ignited thereby. But this combination of conditions is not likely frequently to occur; the second cause above given is therefore more likely to be fruitful of accidents; but the existence of a third cause, to which the majority of explosions connected with blasting in collieries is most probably ascribable, has been very clearly established by the careful inquiries, sound reasoning, and ingenious experiments of Mr. W. Galloway, Inspector of Mines. Mr. Galloway conceived, and has clearly established by experiments in the laboratory and in coal-pits, that the sound-wave established by the firing of a shot (especially by the sharp explosion produced when the tamping is shot out of a hole) will by transmission, even to very considerable distances, have the effect of forcing the flame of a safety-lamp through the meshes of the gauze, and will thus lead to the ignition of an explosive gas mixture surrounding the latter. + It may be hoped that the miner may be trained to a knowledge of the danger he incurs by the incautious use of gunpowder, although the persistent recklessness with which he sacrifices safety to comfort, in despising the use of the safety-lamp, forbids sanguine expectations in this direction. 'Reference has not been made to another very possible source of accidents due to the employment of gunpowder for blasting purposes, namely, carelessness in the keeping and handling of the explosive agent by the men. Personal observation by the lecturer of the reckless manner in which powder is frequently dealt with in mines, leads him to believe that this contributes its quota as a cause of colliery explosions. NATURE, vol. v. p. 504; vol. x. p. 157. † NATURE, vol. x. p. 224. The accidents in collieries have their parallel in domestic life, in coal-gas explosions, which, though at first sight of compara tively small importance if judged by the loss of life and property which they occasion, yet merit serious consideration on account of the great frequency of their occurrence, and the demonstra. tion which they almost always afford of ignorance or culpable carelessness. The circumstance that the admixture of even minute quantities of coal-gas with air can be at once detected by the unmistakable odour of the gas, should serve as a safeguard against accidents; unfortunately, however, thoughtlessness or want of knowledge frequently causes this very fact to lead to the opposite result Escapes of gas in comparatively small quantities often occur at the point of union (generally by a ball-and-socket joint) of a hanging burner or chandelier with the gas-pipe, or at the telescope-joint of such gas-fittings; the column of water required in the joints to confine the gas becoming very gradually reduced by evaporation. In such instances an explosive mixture will accumulate in the upper part of the apartment of which windows and doors are closed, while the air in the lower part will continue for a long time free from any dangerous admixture of gas; and instances are continually recorded in the public prints of the deliberate ignition of such explosive mixtures, by persons who, observing the smell of coal-gas upon entering the room, proceed forthwith to search for the point of escape by means of a flame. It need scarcely be stated that such a test is a perfectly safe one in itself, and that if the acceptance of the warning given by the odour of gas in the lower part of the room were promptly fol lowed by the simple precautionary operation of leaving open for some time all windows and doors, so as to afford ready ingress of fresh air, and thus speedily expel, or very largely dilute the gas-mixture, the leakage could be looked for with no risk of accident. Gas explosions, generally of a serious nature, do occasionally occur through no fault of those who are the direct agents in bringing them about, as by a person entering with a light a closed apartment in which there has been a very considerable escape of gas for some time, or a building in which gas has been entering from a leakage in the supply-pipe or the main. The employment of illuminating agents closely allied to co gas, namely, liquid carbo-hydrogen compounds obtained by the distillation of coal or shale, or derived as natural products from coal-bearing strata, gradually extended during the earlier part of the last quarter of a century until they became formidable rivals of mineral and vegetable oils and even of gas itself. The several varieties of so-called petroleum spirit which are known as naphtha, benzine, benzoline, gasoline, japanner's spint, &c., yield vapour more or less freely on exposure to air at ordinary atmospheric temperatures. and even in some cases below 50 F. Although much the largest proportion of the petroleum spirt employed is probably used in lamps of some form or other, there are other important uses to which it is applied in large quantities, especially in various industries. The so-called paraffin- or petroleum-lamp explosions, of which in the earlier days of the employment of these illuminating agents there were so many recorded in the newspapers, and of which one still hears occasionally, were, with very few exceptions, not correctly designated as explosions, and when they were so, were not caused by the employment of the volatile oils or petroleum spirit. As these vaporise very freely at the slightly elevated temperature which a reservoir of a lamp soon attains, air either entirely expelled from the latter by the vapour, or so diluted by it, that the mixture is not explosive. It therefore flame can have access to vapour escaping from any opening in the reservoir near the wick, in a badly-constructed lamp, it wil merely burn as it escapes. If a lamp charged with petrole spirit be carried incautiously, or accidentally jerked so that the liquid is suddenly brought into contact with the warmer porta of the lamp, near the flame, a very rapid volatilisation may thereby be caused, resulting in a considerable outburst of flame. If a petroleum oil which has been imperfectly refined, and which, therefore, contains some proportion of the very volare products, or spirit, be employed in a lamp, a slight explos may be caused by its yielding up a small amount of vapozz the temperature to which the reservoir becomes heated, and thes producing a feebly explosive mixture with the air in the later, which may become ignited by the flame of the lamp. An e sion thus produced is not at all of violent character, begg generally merely a feeble puff; it may, however, cause the cracking of the reservoir, and the consequent spilling and in SOCIETIES AND ACADEMIES Royal Society, March 18-"On the Behaviour of the Hearts of Molluscs under the influence of Electric Currents." By Michael Foster, M.D., F.R.S., and A. G. Dew-Smith, B. A. The observations were made chiefly on the heart of the common snail. An interrupted current, applied directly to the ventricle (or auricle), and of such a strength as not to cause tetanic contractions, produces, as has already been pointed out, distinct inhibition, altogether similar to that brought about in the vertebrate heart by stimulation of the pneumogastric nerve. Single induction-shocks, of a strength insufficient to cause a contraction, produce no appreciable effect, in whatever phase of the cardiac cycle they are thrown in; but two or more such shocks, the one following the other at a sufficiently short interval, produce a slight inhibition; that is, the succeeding diastole is prolonged. When a constant current of sufficient intensity is thrown into the ventricle at rest, a contraction or "beat" is observed at both the making and the breaking of the circuit. But the initial, making, beat starts from, and is confined to the region of, the kathode, while the final, breaking, beat starts from and is confined to the region of the anode. This is the case whatever be the position of the electrodes. A constant current of sufficient intensity to bring about a making and a breaking beat when applied for, say five seconds, may be applied momentarily without producing any beat at all. The constant current, therefore, requires some considerable time to develop its maximum effect. When a constant current is applied to a spontaneously beating ventricle, a polarisation of the ventricle results of such a kind that the region of the kathode is thrown into a condition which the authors would wish at present not to define more strictly than by saying that it is "favourable to the production of a rhythmic beat," while the region of the anode is thrown into an opposite condition, unfavourable to the production of a rhyth mic beat. On the withdrawal of the current a rebound takes place at either electrode, the kathode region becoming for a time unfavourable to the production of beats, the anode favourable. Of these two conditions, the one unfavourable to the production of beats, whether it be in the anodic region during the passage of the current, or in the kathodic region during the rebound, is more easily produced by slight currents than its opposite. Hence the total effect of a slight current, the balance of the opposing agencies, is unfavourable to the production of the rhythmic beat. Consequently, when a current, as in a single induction-shock, is applied for so short a time that its maximum effect is not reached and no direct kathodic contraction or beat is called forth, the net result is a hindrance to the rhythmic beat, or, in other words, an inhibition, which may be too slight to be recognised with a single shock, but becomes evident when the shock is repeated after a not too long interval, and is very marked when several shocks rapidly follow each other as in the ordinary interrupted current. The main results obtained with the snail's heart were corroborated by observations on the hearts of Sepia and Aplysia. In conclusion, the authors regarding the rhythmic beat of the snail's heart (which they believe contains no differential nervous structures) as a purely protoplasmic movement, call attention to what may be called the principle of physiological continuity, and offer suggestions towards defining the exact function of the intrinsic ganglia of the vertebrate heart, and of other spontaneously beating organs. "On the Liquation, Fusibility, and Density of certain Alloys of Silver and Copper." By W. Chandler Roberts, Chemist of the Mint. Communicated by Dr. Percy, F.R.S. The author states that the most remarkable physical property of silver-copper alloys is a molecular mobility, in virtue of which certain combinations of the constituents of a molten alloy become segregated from the mass, the homogeneous character of which is thereby destroyed. These irregularities of composition have long been known, and reference is made to them in the works of Lazarus Erckern (1650), and of Jars (1774). A very complete memoir was published in 1852 by Levol, who did much towards ascertaining the nature and defining the limits of this molecular mobility. He discovered the important fact that an alloy containing 71 89 per cent. of silver is uniform in composition. Its chemical formula (Ag,Cu,) and peculiar structure led him to conclude that all other alloys are mixtures of this, with excess of either metal. The electric conductivity of these alloys was studied in 1860 by Matthiessen, who doubted the accuracy of Levol's theory, and viewed them as "mechanical mixtures of allotropic modifi. cations of the two metals in each other." The author then describes the experiments he made with a view to determine the melting points of a series of these alloys. He adopted Deville's determination of the boiling point of zinc (1040° C.) as the basis of the inquiry, and ascertained by the method of mixtures, the mean specific heat of a mass of wrought iron between o° C. and the melting point of silver, which, as Becquerel showed, is the same as the boiling point of zinc. The mean of three experiments, which were closely in accordance, gave o 15693 as the specific heat of the iron; and it should be pointed out that this number includes and neutralises several errors which would affect the accuracy of the subsequent determinations. a calorimeter. Melting points of several alloys were then determined by plunging an iron cylinder into them and transferring the iron to These melting points varied from 840° C. to 1330° C., or through a range of 490° C. The alloys which occupy the lowest portion of the curve contain from 60 to 70 per cent. of silver. The results are interesting, as they show that the curves of fusibility and electric conductivity are very similar. Mr. Roberts then describes experiments in which alloys were cast in red-hot moulds of firebrick, the metal (about 50 oz.) being slowly and uniformly cooled. The results of these experiments on liquation are elaborate, and cannot be given in a brief abstract. The density of pure silver and of Levol's homogeneous alloy, while in the fluid state, were then determined by the method described by Mr. Robert Mallet, the metals being cast in conical vessels of wrought iron. The results obtained were as follows: Density fluid. 9'4612 9'0554 Density solid. 10'57 9'9045 In the case of silver, the mean linear expansion deduced from this change of density is co003721 per 1° C., which is nearly douple the coefficient at temperatures below 100° C. Physical Society, March 13.-Dr. J. H. Gladstone, F.R.S., president, in the chair.-Mr. W. Chandler Roberts read a paper on the electro-deposition of iron. He referred to the beautiful specimens of electro-iron, the work of M. Eugène Klein, a distinguished Russian engineer and chemist, which were exhibited at the meeting of the British Association at Exeter. In 1870 Mr. Roberts visited St. Petersburg, and had the advantage of receiving from the late M. de Jacobi suggestions which enabled him to deposit iron with much success. He stated that a plate of electro-iron 150 mm. square by 2 mm. thick, was deposited on copper, by Herr Bockbushmann, in 1846. In 1857, M. Feuquières exhibited specimens of electro-iron at the Paris Exhibition. In 1858, M. Garnier patented in England his process, termed aciérage, for protecting the surfaces of engraved copper-plates; and in the same year Klein produced the admirable works above referred to. The author then exhibited specimens which he had obtained by Klein's method. The bath consists of a double sulphate of iron and magnesia, of sp. gr. 1155; the chief conditions of success being the neutrality of the bath and the em. ployment of a very feeble current. Iron so obtained possesses a higher conductivity than any commercial iron (Matthiessen), its sp. gr. is 8.139, and its occludes thirteen times its volume of hydrogen. A tube of the metal deposited on a rod of wax, which was vacuum-tight at the ordinary temperature, allowed hydrogen to pass freely at a dull red heat.-After a brief discussion, Prof. Guthrie described some experiments which he has recently made, with the assistance of Mr. R. Cowper, in continuation of former researches, on salt solutions and attached water. The main object of these experiments was to ascertain the manner in which mixtures of salts act as cryogens, and to study their combination Proc. Roy. Scc., vol. xxiii. p. 209. with water at various temperatures and in various proportions. When two salts to which either the acid or the base is common, and which do not form a double salt, are mixed in equivalent proportion, the cryogen produced has nearly the temperature due to the salt, which alone would produce the greatest degree of cold. Solidification begins at a temperature below the melting-point of the least fusible, and continues at lower and lower temperatures until the temperature due to the other constituent salt is reached. Occasionally a cryohydrate having a constant solidifying point has been obtained by mixing in definite proportions salts which are not known to exist in the form of a double salt. In all such cases the solidifying point of the mixture is intermediate between the solidifying points of the constituents, and its temperature as a cryogen is also between the temperatures of the constituents when separately used as cryogens. When two salts composed of different acids and bases are mixed, and no precipitation occurs, it is generally considered that partial double decomposition takes place, two new salts being formed. It was found that if the salts AX and BY be mixed in atomic proportion and dissolved in the smallest possible amount of water, a mixture identical with that produced on mixing AY with BX is obtained. The temperature and composition of the resulting cryohydrate are the same in both cases. But the temperature never falls as low as the point which could be reached by employing whichever of the salts A X, AY, BX, BY, forms a cryohydrate with the lowest temperature. Thus a saturated solution of a mixture of nitrate of potassium and sulphate of sodium solidifies at 5° C. A mixture of nitrate of sodium and sulphate of potassium also solidifies at this temperature. Since the solidifying point of nitrate of sodium is - 17°, this salt cannot exist without partial decomposition taking place in either mixture; for, as has been shown above, its presence would ultimately depress the solidifying point. Dr. Rac remarked that these researches are specially interesting in connection with the salts retained by sea-ice. With a view to study this subject, he has already requested captains of whalers visiting the Arctic regions to bring home samples of ice of different age and from various localities. PARIS Academy of Sciences, March 15.-M. M. Frémy in the chair. The following papers were read:- On electro-capillary action and the intensity of forces producing it, by M. Becquerel (fourth paper on the subject).-A note by H. Sainte Claire Deville, on the alloys of platinum and iron.-Researches on the fatty acids and their alkaline salts, by M. Berthelot. The subject is treated at length, and the formation of sodium, ammonium, and barium salts, both in solution and in the solid state, is considered. -On acetic anhydride, by the same; account of new experi ments to determine the heat evolved during the transformation of acetic anhydride into acetic acid.-A note by M. de LecazeDuthiers, on the origin of the vessels in the tunica of simple Ascidia. On the simultaneous formation of several mineral species in the thermal source of Bourbonne-les-bains (HauteMarne), specially of galena, anglesite, pyrites, and silicates of the zeolite family (notably of chabasite), by M. Daubrée (second paper).--On a peculiar mode of excretion of gum arabic, by the Acacia Verck of the Senegal, by M. Ch. Martins.-Report by M. Milne-Edwards, on the measures proposed to prevent the invasion into France of the American insect Doryphora, which destroys the potatoes.-M. Mouchez, the chief of the expedition sent to St. Paul to observe the transit of Venus, was then received by the President, who welcomed him in the name of the Academy. M. Mouchez read a long paper on the subject, giving all the details of the transit. He specially described the optical phenomena observed in the vicinity of the contacts, and brings home no less than 489 photographic proofs that can all be utilised for micrometrical measurements. The two interior contacts were observed with great precision, the two outer ones having been rather spoiled by clouds. Altogether this expedition may be considered highly successful.-On the geometrical solution of some new problems relating to the theory of surfaces, and depending upon infinitesimals of the third order, by M. Mannheim (second paper).-On the simplest modes of limit equilibrium which can be present in a body without cohesion and strongly compressed; application to a mass of sand filling the angle between two solid planes and movable round their line of intersection as axis; by M. J. Boussinesq.-A memoir on the formula of perturbation, by M. Emile Mathieu.--Micrographic study on the manufacture of paper, by M. Aimé Girard.-On the action of sulphate of ammonia in the culture of Leet-root, by M, P. Lagrange.-A note by M. F. Fouqué, on the nodules of wollastonite, fassaite pyroxene, melanite garnet of the Santorin lava.-On the immediate treatment of intestinal obstruction, by the aspiration of the gases from the intestines, by M. Demarquay.-A memoir, by M. Michal, on the determina. tion of the results of several observations, with special reference to the precision of the result.-A note, by M. L. Berthout, on the discovery of a deposit of fossils in the plain of Ecouche, in the arrondissement of Argentan (Orne).-A number of members then made various communications on Phylloxera.-The Minis ter of Public Instruction addressed to the Academy a project of a medal in commemoration of the Transit of Venus.-The Minister of Public Works sent a report of the Commission charged with the proposal of measures to be adopted to prevent the infection of the River Seine in the neighbourhood of Paris.On certain left perspectives of plane algebraic curves, by M. Halphen.-On some properties of curves traced on surfaces, by M. Ribaucour.-On diffraction and the focal properties of nets, by M. A. Corna.-On the magnetising function of tempered steel, by M. Bouty.-On the determination of the quantity of magnetism in a magnet, by M. R. Blondlot.-On the theory of storms; a reply to M. Faye, by M. H. Peslin. M. Faye, who was present, then made some observations on the same subject.-On some double stars whose motions are rectilinear, and are due to a difference in proper motion, by M. C. Flammarion.-On the identity of the bromo-derivatives of the hydrate of tetrabromethylene with those of perbromide of acetylene, by M. E. Bourgoin. On the quantities of heat evolved in the decompo sition of the chlorides of some acids of the fatty series, by M. L. Longuinine, specially referring to butyric, isobutyric, and valeric acids. On amylogene, or soluble starch, by M. L. Bon. donneau. -On a new method of volumetric analysis of liquids, by M. F. Jean.-Chemical researches on the absorption of the ammonia of the atmosphere by the volcanic soil of the solfatara of Puzzola, by M. S. de Luca. -A reply to two recent commu nications of M. Béchamp, relative to spontaneous alterations of eggs, by M. U. Gayon.-Observation of the life of Heloderes horridum, Wiegmann, by M. Sumichrast, reported by M. Bocourt.-On the helminthological fauna of the coasts of Bri tany, by M. A. Villot.-Critical observations on the classification of Paleozoic Polyps, by M. G. Dollfus.--MM. Dumay and Martin de Brettes then made some communications relating to the bolide seen on February 10 last.-A note, by M. Neyreneuf, u the combustion of explosive bodies.-A number of scientác works were presented to the Academy by several gentlemen. D A Gyrostat Problein-Answer (With Illustration) —D. M'FArlank 424 The Law of Muscular Exhaustion and Restoration.-G. HINRICHS 10 Accidental Importation of Molluscs and Insects.-Dr. F. BUCHANAN Fall of a Meteor at Orleans.-HERBERT M'LKOD 427 THE NEW STANDARD SIDEREAL CLOCK OF THE ROYAL OBSERVATORY, GREENWICH (With Illustrations) 437 ARCTIC VEGETATION NOTES ACCIDENTAL. EXPLOSIONS. By Prof. F. A. ABEL, F.R. S. SOCIETIES AND ACADEMIES BOOKS AND PAMPHLETS RECEIVED ERRATUM.-Vol ai. p. 403, col. 2, lines 10 and 11 from butt a, it "work" read "rock." |