I have always been impressed with the strikingly inferior brightness of Mercury as compared with Venus; and as such a condition is the very reverse of what might be expected by reason of Mercury being so much nearer to the sun than Venus, I awaited the rare event of a very close conjunction of these two planets that occurred on September 26 and 27 last. With the advantage of a perfectly clear sky I had the two planets before me for several hours, so to speak, side by side in the field of the telescope at the same time, thus affording me a most perfect opportunity for making a comparison of their relative brightness. It is difficult to convey in words an exact impression of the difference in the brightness of such objects, but I may attempt to do so by stating that Venus looked like clean silver, while Mercury looked like lead or zinc. Were I to indicate my impressions by way of number I would say that Venus was fully twice as bright as Mercury. So remarkable an inferiority in the brightness of Mercury, notwithstanding his much greater nearness to the sun, appears to me to indicate the existence of some very special and peculiar condition of his surface in respect to his capability of reflecting light-a condition that may be due to the nature of his envelope, if such exist, or of that of his surface, by which the fervid light of the sun's rays falling on him are in a great measure quenched or absorbed so as to leave but a small residue to be reflected from his surface. If this be so, it appears to me to be reasonable to suppose that the absorption of so much light must result in a vast increase in the heat of the surface of Mercury beyond what would have been the case had Mercury possessed the same surface conditions as Venus. Whether in the progress of spectroscopic investigation we shall ever be enabled to detect some evidence of metallic or other vapours or gases clinging to or closely enveloping the surface of Mercury that might in some respect account for so remarkable an absorption of the sun's light, we must be content to await the acquirement of such evidence if it ever be forthcoming. It appears to me, however, to be well to raise such a question, so that our astronomical spectroscopists may be on the outlook for some evidence of the cause of so very remarkable a defective condition in the light-reflecting power of Mercury to which I have thus endeavoured to direct attention."-On the water of Thirlmere, by Harry Grimshaw, F.C.S., and Clifford Grimshaw.

PARIS

to

Academy of Sciences, October 28.-M. Fizeau in the chair.-M. De la Gourmerie read a note on the works of the late M. Bienaymé.-The following papers were also read :-On the decomposition of hydracids by metals, by M. Berthelot. The heat of formation of gaseous chlorhydric acid from its elements is surpassed by that of all anhydrous chlorides, even chlorides of lead, copper, mercury, and silver; gold is the only exception among ordinary metals. The inference that all these metals, except gold, must decompose chlorhydric gas with liberation of hydrogen, is confirmed by experiment. Platina and palladium, also, their chlorides having low heats of formation and little stability, did not decompose chlorhydric gas up 550%-On Vice-Admiral Cloue's "Pilote de Terre Neuve," by M. Faye. On the state in which carbonic acid exists in the blood and the tissues, by M. Bert. The escape of carbonic acid during the respiratory act requires a dissociation of the super-carbonised salts of the blood. These salts were saturated with carbonic acid neither in the arterial nor the venous blood, nor in the tissues. The life of the anatomical elements can only be maintained in presence of carbonic acid in the state of combination. When the alkalis are saturated, and this gas appears in excess in the state of simple solution it rapidly causes death.-Influence of the nervous system on the phenomena of absorption, by M. Moreau. He attached to the dorsal fins of fishes that had swimming bladders a small glass balloon, lighter than the water, and in a few hours the volume of the fish had diminished through absorption of a part of the air contained in the bladder. When a piece of metal was substituted for the balloon, the volume of the fish increased. There is thus a sensation of thrust upwards or downwards, and it is under influence of the former that absorption of air in the bladder takes place, probably through a reflex action. -On decipium, a new metal of samarskite, by M. Delafontaine. In the samarskite of North Carolina he finds yttria, erbine, terbine, philippine (yellow (PPO), equiv. about 90; characteristic absorption band about 449 in λ), decipine (white (DPO), equiv. about 122, band 416); thorine and oxides of didymium and cerium. The equivalents of the metals in some of these earths are shown

to present interesting numerical relations. Decipium is so ca from decipiens, deceiving. The didymium of cerite is prob a mixture of several bodies, by M. Delafontaine. This is b on spectral observations.-Reply to a recent communication M. Hirn, on a gyroscopic apparatus, by M. Gruey.-Cl, fication of double stars, by M. Flammarion. Of the 11 double or multiple stars discovered, he finds there are only that give certain indications of a relative motion of the c ponents. These groups are divided into 731 doubles, 73 trip 12 quadruples, 2 quintuples, and I sextuple, in all 1,745 variously associated. Of these couples in motion 558 1 been found with orbital systems, and 316 whose compon have been connected merely by the chance of celestial spectives and form optical groups. In the orbital syst there is a preponderance of retrograde motion from ne to south by west (Several other facts are given.). the integration of the equation (1) Ay' + Byy + Cy Dy' + Ey + F = 0, by M. Alexeeff.-On involution in curof n degree, by M. Serret.-Remarks on two integrals obtais by Lamé in the analytical theory of heat, by M. Escary.ply to an observation of M. Boltzmann, by M. Lévy.-On magnetisation of tubes of steel, by M. Gaugain. When a ! tem formed of two parts having different coercive forces is s jected to action of a weak current, the part having the least co cive force is always that which takes the strongest magnetisat (whichever its position, tube, or core).-On a telephone call, M. Perrodon. This consists in connecting a Ruhmkorff with the plate of the telephone, so as to get a loud continu sound. On the transformation of valerylene into terpilene, M. Bouchardat.-Artificial reproduction of melanochroïte, M. Meunier. This is by keeping fragments of galena in dil aqueous solution of bichromate of potash.-On the eliminat of salicylate of soda, and the action of this salt on the heart, m MM. Blanchier and Bochefontaine. It stimulates various sec tions, notably the salivary. In man it is at once expelled the kidneys (appearing in the urine in 20 mm.); in the dog appears both in the urine and the saliva, also in the bile as pancreatic fluid. The hypersecretion of saliva is due to act of the salicylate on the grey substance of the central nerv system. In strong doses, the salt stops the heart in diastole On parthenogenesis in bees, by M. Sanson.

THE

HE statements recently made in the Times respecting the stability of Cleopatra's needle and the maximum intensity of the pressure of the wind in this country have awakened much interest, if not anxiety, about the subject. The appearance of the lofty obelisk balanced on so small a base suggests to many the thought of an egg standing on its end, and presents every idea of instability. This idea is much amplified by a very erroneous estimation, we believe, by most persons of the real dimensions of the base; we have heard this estimated at various diameters down to two feet, but in reality it is in no direction less than five. The statement that the stability of the obelisk is sufficient to withstand a wind pressure of 80 or 90 lbs. per square foot having been made, the storm from Liverpool at once broke on it and upset people's minds, if not the monolith. Thus we learn, from the observations taken by Mr. Hartnup, the astronomer at the Liverpool Observatory, that on January 30, 1868, "it began to blow strongly about 9 A.M., and from that time gradually increased in violence until halfpast II P.M. on the 31st, when there was one gust of wind which registered 51 lbs. on the square foot. From this time the gale rapidly increased till noon next day, blowing with a severity quite unprecedented in this country. The anemometer which has been erected at the Bidston Observatory is made to register up to 60 lbs. on the square foot, the idea being that no gale would reach that degree of violence. Between eleven o'clock and one o'clock, however, the registering pencil was driven far beyond this limit, and Mr. Hartnup calculated that at several periods the pressure could not have been less than from 70 lbs. to 80 lbs. on the square foot. The anemometer was erected in 1851, and the most severe gale registered up to this time was in December, 1863, when there were three gusts which registered 45 lbs. to the square foot." Further details respecting this remarkable hurricane will be found in the Journal of the Scottish Meteorological Society, from which we find

is much in excess of the true value. Mr. John Dixon in his letter to the Times on the subject gives a good illustration of a pressure of 80 lbs. to the square foot by comparing it to the weight on the floor of a densely-crowded room. It has been ascertained by experiment that the weight of a crowd of persons can attain 80 to 120 lbs. per square foot, the latter figure being reached only when the experiment was made with labourers of above the average stature packed as closely as possible, and the former being commonly taken as the maximum load to which the platform of a bridge can be subjected by a dense mixed crowd. Thus Mr. Dixon remarks, "the windows of a building certainly have to bear an equal strain with the walls, and I suppose it would be immaterial to the glass whether it was placed vertically or horizontally. A densely packed crowd hardly weighs 80 lbs. per square foot of the space it stands upon. Reduce therefore the theory to common sense; would any one dream of standing on a floor formed of glazed window sashes?" On the whole we rather think not, even if, to make the case analogous, means were taken to distribute the pressure uniformly, and we are forced to the conclusion that either the Bidston Observatory is a very strongly constructed building with window-sashes and glass of unusual strength, or that the anemometers are untrustworthy.

Leaving now the question of the maximum pressure of the wind to be decided by meteorologists, there remains to be ascertained what that pressure would have to reach on the banks of the Thames to endanger the existence of the obelisk. Mr. Dixon's assurance has probably set the fears of many at rest; he says: "As to its stability there need be no fear-130 lbs. of wind-pressure would not upset it. The columns of the Times are not the place to ventilate calculations and figures." We can assure Mr. Dixon that these calculations would be of sufficient interest to the readers of NATURE to find a place in its columns, but in their absence we are obliged to fall back on our own. The widths of the top and bottom of larger face of the obelisk are respectively 64 inches and inches, the height being 60 feet 6 inches exclusive son me idal point, which would be 7 ft high if intact; assuming then, an additional foot of height for the fover rounded end, the moment the prossuro the area of the

miles of wind passed the observatory, giving a velocity

of 1 lb. on the square foot. The

eight of the stone is on the assumption of per

of 35 lbs. to the square foot, while the strongest gusts registered 42 lbs. on the square foot. At Edinburgh the gale was more severe than at the latter place; cabs and horses are said to have been blown over, but there is no record of the pressure or velocity as there was unfortunately no anemometer in working order. Many authorities state that the maximum pressure of the wind does not exceed 55 lbs. to the square foot in this country, and as this is the figure commonly assumed by engineers in the design of large structures, it is of the greatest importance that the trustworthiness of the Bidston anemometers should be ascertained. Pressure anemometers are obviously liable to errors from the varying modulus of elasticity of their springs and the momentum of their moving parts and supports, while Robinson's anemometers may give a maximum velocity due to small eddies, which VOL. XIX.-No. 472

fect rigidity, the ultimate stability radius of base (2·5), and the corresponding wind pressure 196 X 2.5 X 2240 84.88 lbs. per square foot. But

12,931

=

the material of the obelisk not being perfectly rigid, it will be seen that this ultimate stability could not be reached. The effect of the wind-pressure is to cause a deviation of the line of action of the resultant pressure on the base from its centre with a diminution of the stress on the windward, and an increase of that on the lee-side of the base; if the decrease exceeds the normal pressure due to the weight the joint will tend to open, while if the increase is carried too far it may reach the crushing strength of the material.

Both these effects have to be considered. Now in the design of masonry work of a substantial character it is

C

the usual engineering practice to so distribute the stresses that no joint tends to open under the most unfavourable conditions, though this condition is doubtless frequently neglected in flimsy structures. In order that this condition should be fulfilled, the resultant of the pressure on the base must not deviate from the centre of gravity of the base by a quantity greater than x' given in the I equation x' = where is the moment of inertia of Xs' the base about the neutral axis or line through its centre of gravity perpendicular to the direction of the deviation of the resultant, S the area of the base, and X the greatest distance of a point in the base from the neutral axis on the side of the greatest pressure. In the case of

==

diameter of base 8

=

The wind pressure 196 X 625 X 2240 12,931

=

*625 feet in corresponding

a circular base ' the present instance. to this deviation = = 21°22 lbs. per square foot. When the wind-pressure exceeds this amount there is still the tensile strength of the cement with which the stone is bedded to resist the tendency of the joint to open on the windward side. While the introduction of a layer of cement under the stone doubtless adds to its steadiness under a wind-pressure of 30 or 50 lbs. to the square foot, it would add a very serious element of danger should the pressure ever approach that recorded at the Bidston Observatory, as the cement on the lee side would probably then be subjected to a crushing stress in excess of its strength, and by giving way would cause the column to heel over to some extent; in fact, if there was any probability of that wind-pressure being reached, it would have been safer to have omitted the cement and trusted for the ultimate stability to the far greater resistance to crushing of the granite. It would be impossible, without making assumptions unfounded on experiment, to estimate with any accuracy the value of the additional stability given by the cement in the case of moderate wind-pressures. We have, however, calculated the conditions of equilibrium, neglecting the tensile strength of the cement, as well as the bending of the stone.

On this assumption we find that a wind pressure of 50lbs, per square foot would cause the joint to open on the windward side as far into the base as the centre; the column would thus be standing only on, the leeward half of its base, but the stability would not be endangered by this as the maximum pressure on the base at its outer edge would only amount to 40 tons per square foot, which is less than the crushing strength even of the cement. The line of the resultant pressure on the base would be at a distance of 1'472 feet from the centre, if the bending of the column is disregarded. To take into consideration the flexure of the column would involve too long calculations for our present purpose, even if the modulus of elasticity of granite had been determined with sufficient accuracy to make the results of any value, but this we believe has not yet been done. The conclusions we arrive at are as follows:-As long as the foundations remain secure, the obelisk may be frequently subjected to a wind pressure of 21 lbs. per square foot without the slightest tendency to accident; if subjected at long intervals to a pressure of 40 or 50 lbs. to the square foot, it would

probably stand for an indefinitely long period until the fatigue of the cement under variations of stress or its natural decay, if that ever takes place, causes its rupture, but under a pressure of this intensity it must be borne in mind that considerable oscillation would take place, and that if the period of the gusts nearly agreed with the time of vibration of the stone it might be overturned; while if a pressure of So lbs. per square foot is reached it is very questionable if the survivors among the inhabitants of the neighbourhood will find it in situ when they have time to go and look for it.

DRAPER'S SCIENTIFIC MEMOIRS Scientific Memoirs: being Experimental Contributions to a Knowledge of Radiant Energy. By John William Draper, M.D., LL.D. (London: Sampson, Low, and Co. New York: Harper Brothers, 1878.)

THE

HE scientific world is to be congratulated on the accession to its literature of these memoirs constituting as they do a distinct historical sketch of the works of a physicist who is at once an ardent experimentalist and a careful theorist. As he remarks in his preface, many of his results of experimental investigation on scientific topics have been largely disseminated in European languages, and many of the conclusions they have presented have been admitted into the accepted body of scientific knowledge. The papers in which these results were published have, however, appeared from time to time in various American and English periodicals, but we now have them collected in a form in which they are accessible and convenient for reference.

The four opening memoirs seemingly occupy their position in the volume for the purpose of calling the attention of the reader to the fact that a large portion of the subject that Kirchhoff treated mathematically in a paper which appeared in Poggendorff's Annalen in 1860, and which at the time was considered the foundation of spectrum analysis, had already been experimentally proved and published by our author some thirteen years before. The theorist apparently ignored the work of the experimentalist, and the claim of the one to priority in regard to the enunciation of certain fundamental principles of spectrum analysis is now on the best of evidence disputed by the other. The titles of these first four memoirs and their dates of original publication will give an idea of the indictment framed against Kirchhoff which appears in a note appended to the last of them. They are—

I. Examination of the radiations of red-hot bodies. The production of light by heat, published in 1847.

II. Spectrum analysis of flames. Production of light by chemical action, published in 1848.

III. On invisible fixed lines in the sun's spectrum detected by photography, published in 1843.

IV. On the nature of flame, and on the condition of the sun's surface, published in 1858.

Controversy regarding priority of discovery is always distasteful, and the indictment against Kirchhoff is a heavy one, but the offence might have been charged also against those scientific writers who, careless of history, have been accomplices in doing Draper an injustice. But turning to the more agreeable side of the subject of these memoirs we find that Draper fixed the temperature at which solid

rine and hydrogen when acted upon by radiations, but that he also used it practically, though not with such nicety of method as subsequently employed by Bunsen and Roscoe. He also invented the ferric oxalate photometer, dependent on the reduction of this ferric compound to the ferrous state and the liberation of carbonic acid. In both of the foregoing we have a measure of the quantity of the radiations which these mixed gases, or solution, select. On this particular subject of selective absorption, when chemical action takes place, Draper experimented most fully. He showed, for instance, that the sensitiveness of the surface of a Daguerreotype plate is at its maximum when of a yellow tint, owing to the absorption of the blue rays, and conclusively shows that when it is of a blue tint that these same rays are largely reflected. In fact, he announced, with all the authority of a successful experimentalist, that for the production of chemical action in a compound by any particular ray, the absorption of that ray by the compound was an absolute necessity. In late years we have had several rediscoveries of this important truth, and probably it will be rediscovered again and again, notwithstanding the publication of these memoirs.

We have not space to do more than to mention the memoirs on the "Distribution of Heat in the Spectrum," on "The Chemical Force in the Spectrum (both titles of which, by the by, are inexact, as Draper himself was the first to prove), and on "The Supposed Magnetic Effects Produced by the Violet Rays,” all of which are important contributions to science, as are also those on "The Cause of the Flow of Sap in Plants, and the Circulation of the Blood in Animals," and "On the Decomposition of Carbonic Acid Gas by Plants in the Prismatic Spectrum." All these have been treated in a masterly manner, and the results lucidly and tritely recorded. Reading these memoirs leads us to the conclusion that we have in Draper a successful

experimenter, who has been perhaps too little appreciated in the world owing to his too great modesty in neglecting

to call attention to the facts he has observed, and to claim for himself honour where the honour was due.

Like other men of mark in science, the ardent pursuit of it was undertaken through what might be termed an accident. He tells us in his preface that happening to see a glass containing some camphor, portions of which had been caused to condense in very beautiful crystals, he was induced to read everything he could obtain respecting the chemical and mechanical influence of light, adhesion, and capillary attraction; the experiments he made in connection with these subjects being contained in the volume before us. His thoughts being thus directed to physiological studies, he published papers on these topics in the American Journal of Medical Sciences, which created such a favourable impression that he was appointed, in 1836, Professor of Chemistry and Physiology in Hampden Sidney College, Virginia. He afterwards was appointed to a similar chair at New York University, which, we believe, he at present holds.

It would be travelling out of our province to do more than call attention to Dr. Draper as the author of "A Treatise on Human Physiology," ," "The History of the Intellectual Development of Europe," "The History of

the American Civil War," and of "The History of the Conflict of Religion and Science," works which have met with well-merited success, and which show the varied bent of his mind.

The history of the Rumford medal fund held in trust by the Royal Society, and the awards made by this body are too well known to need repetition; but it is not equally well known that a similar medal fund was founded in the United States by Rumford, and is held in trust by the American Academy of Arts and Sciences. The medals were to be awarded for "the most important discovery or improvement relating to light and heat that had been made during the preceding two years in any part of America." The awards of the American Rumford medals have been made few and far between, and till 1876 may be said to have been given for inventions rather than discoveries. At this date the medal was awarded to Dr. Draper (as the medal itself records) "for researches on radiant energy." Had he been an European there can be little doubt but that he would have received one of our English medals years ago, and that his name would have been in the same list with those of Leslie, Fox Talbot, Fresnel, and Faraday. As it is he has the honour of being the first recipient of the American Rumford medal which has ever been awarded for pure scientific research.

A CATECHISM OF BOTANY

A First Catechism of Botany. By John Gibbs, of the Essex and Chelmsford Museum. (Chelmsford: Edmund Durrant and Co. London: Simpkin, Marshall, and Co.)

survival of a method of instruction which was very THIS little book is in its way quite a curiosity. It is a popular in its day, but which it is to be hoped-notwithstanding that Magnall's “Questions" is still said to be a good property—even in country towns like Chelmsford, is on the road to extinction. Catechisms originated in the necessity of giving some uniformity and precision to oral religious instruction. Their great merit is of course that they remove all responsibility from the teacher, and merely require that their formulæ should be taught with patience and perseverance. They render unnecessary, indeed even undesirable, any knowledge of the subject on the part of the teacher, and hence it is easy to see the reason of their popularity amongst persons engaged in education, and who, possessed of no scientific training, are yet anxious to get credit for teaching scientific subjects. Mr. Gibbs has evidently felt some uneasiness on this head, and points out accordingly in his preface that :

examination of the plant itself in all its parts to which "The answer to every question may be verified by reference is made. Only in such a way can this catechism be made useful, and by such criticism its value will be ascertained."

But the insidious influence of the purely dogmatic method makes itself but too evident in the next sentence, which is surely the strangest ground of recommendation ever urged for a scientific book :

"In its original form it was admitted to the International Exhibition of 1871, which contained nothing but what the Committee of Selection approved as excellent."