given any proof that such is the case. He says:" We may never in our waking hours be wholly free from the stimulation of the senses, but in the exuberance of nervous power, our activity is out of all proportion to the actual solicitation of the feelings." What is the right proportion of activity to feeling? the proportion that Prof. Bain takes as his standard by which to discover that at times our activity is out of all proportion to feeling. Is not the simple and the whole fact this, that the amount of bodily movement that goes along with a given amount of feeling is different in each individual, and in the same individual from hour to hour. He continues:"The gesticulations and the carols of young and active animals are mere overflow of nervous energy; and although they are very apt to concur with pleasing emotion, they have an independent source? their origin is more physical than mental." Is not the origin not of these only, but of all movements, entirely physical, though it is also a fact that some movements, and certainly these among the number, concur with pleasing emotion? Mr. Darwin has instanced the frisking of a horse when turned into an open field, as an example of joyful expression; on which it is remarked, this "is almost pure spontaneity it does not necessarily express joy or pleasure at all. How curious! One must really be a psychologist before he can see common things in such an uncommon light. Perhaps no movement necessarily expresses any state of consciousness whatever: but no ploughboy, we venture to think, ever doubted that the frisking of his horse, when he turned it loose in the field, was an expression of delight. But, then, ploughboys have no theories about spontaneous activity. All mental states correspond to certain physical conditions; that the nerve-centres and the muscles shall be fresh and vigorous" is the physical condition of much bodily activity, and at the same time of the pleasure that goes along therewith. Granting that "the kitten is not seriously in love with a worsted ball," it thoroughly enjoys the sport nevertheless. Its amusement being mere play does not preclude its being real pleasure. And if our memories can be trusted, the worsted balls of our childhood were far more delightful than the gold and substantial realities we seriously love in our old age. S.

"LAHORE TO YARKAND" Lahore to Yarkand. By Geo. Henderson, M.D., and Al'en O. Hume. (L. Reeve & Co.)

many and severe; the desert nature of the road between the districts of Ladak and Yarkand made it almost necessary to discontinue the expedition, and the great heights that had to be surmounted put a check on rapid progress, in some parts rendering it impossible.

Several opportunities occurred for the observation of the physiological effects of higher altitudes and rapid changes of barometric pressure, one pass near Gnishu which had to be traversed, named Cayley's Pass after Dr. Cayley its discoverer, being 19,600 feet above the level of the sea. From Dr. Henderson's remarks, however, it appears that mountain sickness is not dependent on the rarity of the air alone, for during the time that the expedition was in the pass mentioned, no note was recorded of any of the number suffering from it, whilst previously, on the Chang-la, which is 18,000 feet, most of the camp suffered from severe headache, nausea, prostration of mind and body, together with irritability of stomach and temper; nevertheless observations at the time showed that the pulse was not unusually rapid and the respiration was but little, if at all, increased. The feeling of suffocation occasionally experienced on waking during the night usually passed off after a few deep inspirations had been made. It is much to be regretted that, with the opportunities of verifying and extending Dr. Marcet's observations on the effects of ascending and descending mountains, Dr. Henderson was not in a position to do so, which he undoubtedly would have done if he had been acquainted with them.

Shortly after leaving Patsalung, and when on the southern boundary of Hill Yarkand, “nearly ten miles of the way was over a plain about five miles wide, which was covered to a depth of many feet (in one place where cracks existed, to not less than twenty feet) with sulphate of magnesia (Epsom salts), pure and white as newlyfallen snow." This shows the abundance of a magnesian limestone in the surrounding higher ground, and as the water-supply of the city of Yarkand was from rivers which rose in this or similar hills, the author's remark that "about every third man we saw was afflicted with goître," is scarcely more than was to be expected, and we think that if, instead of making "over to the Dád Khwah a quantity of iodine, for the treatment of goître, at which he was very much pleased," he had proposed a change in the water-supply, the Yarkandis would have been the gainers in the long run.

As the Atalik Ghazi was away at the time Mr. Forsyth arrived at his destination, and as the latter had strict

which they describe, the authors dedicate this handsome volume, which, instead of being a continuous narrative, is divided into three separate parts, each of which will appeal to a different class of readers. The description of the route, and the incidents encountered on it, are given by Dr. Henderson, who with Mr. Forsyth and Mr. Shaw were the only Europeans that went to Yarkand on this "friendly" visit, sent by our Government to the Atalik Ghazi; it occupies two-fifths of the work. The natural history of the living forms met with, mostly by Dr. Hume, fills about one-fourth; the rest consisting of meteorological observations taken by Dr. Henderson on the journey.

The difficulties that had to be encountered en route were

unsuccessful. The return journey being later in the year, the cold and discomfort were greater than on the march north; an idea may be formed of the acuteness of the cold from the author's note on the Sukat pass. "My ink was constantly hard frozen, and on several occasions when I thawed it before the fire and attempted to write in my pencil notes, it froze at once on the point of the pen. Several times I tried to photograph, and once or twice succeeded, but usually the tepid water used for washing the plate froze as I poured it from the jug, and instantly destroyed the picture."

The illustrations of scenery, which in many books of travel are but indifferently drawn, and disappointingly inaccurate, are in this work replaced by "heliotype prints "

from photographic negatives taken by Dr. Henderson himself, and nothing can, in most cases, be more satisfactory. What is wanted on such occasions is not only a picture, but a representation sufficiently full of detail to enable the reader by simple inspection to form a truthful idea of the country described. Such are found in the photographs of the Valley above Paskyum, and the fort and bridge over the Indus river at Kalsi, and others before us, which, from the contrasts of light and shade, and the evident glare, bring vividly before the mind the intensity of the heat, as well as the desolateness of the locality, a combination scarcely possible in any character of engraving.

The Natural History notes are mostly ornithological and botanical. In his résumé of the ornithological results of the expedition, Mr. Hume informs us that "altogether, 158 species were observed, but of these only 59 pertain to the ornithologically unknown hills and plains of Yarkand. ... Of these fifty-nine species, 7, Falco hendersoni (? F. milvipes, of Hodgson), Saxicola hendersoni, Suya albo superciliaris, Podoces hendersoni, P. humilis, Galerida magna, and Caccabis pallidus, are probably new to Science." An excellent illustration, by Mr. Keulemans, is given of each of these new species, except the last, which is very closely allied to C. chukar, and the coloration of the drawing of Sturnus nitens (Hume) exemplifies very successfully the propriety of the specific name. Gould's description of S. purpurascens is compared with that of the new species, the former being absolutely speckless and much smaller. Podoces hendersoni and P. humilis are both new species of this genus, which the author, following Bonaparte, places with the Choughs and not with the Jays and Magpies, remarking, however, "remembering their ground-feeding, dust-loving habits, ... I cannot avoid the suspicion that these birds may constitute a very aberrant form of the great Timaline group."

Mr.

On the Chang-la pass above referred to, Mr. Shaw obtained a butterfly, which Mr. H. W. Bates places in the mountain genus Mesapia, naming it M. shawii; it closely resembles M. peloria. Several specimens of the moth, Neorina shadula were also obtained.

Dr. Hooker and Mr. Bentham have written the descriptions of the new species of flowering plants, which are figured; they include, from the Tamaricaceæ, Hololachne shawiana; from the Compositæ, Iphiona radicta and Saussurea ovata; and from the Apocynaceae, Apocynum hendersonii. Dr. Dickie of Aberdeen describes the Algae and Diatomaceæ, and has also named some new forms.

OUR BOOK SHELF

The Internal Parasites of our Domesticated Animals. By T. S. Cobbold, F.R.S. (The Field Office.)

IN this short and concise work Dr. Cobbold has embodied a series of articles which have appeared from time to time in the Field. They, having been originally written for the perusal of the non-scientific public, are put in a simple and elementary manner, and much stress is laid on the practical bearing of the science of helminthology, the true value of which the author clearly shows to be but little appreciated by the growers of stock. Several excellent illustrations accompany the descriptions, which

will greatly assist the amateur reader. The entozoa infesting the ox are first described,-flukes, tapeworms, and The importance of measle, together with round worms. more perfect sewage arrangements whereby the ejecta of one animal are not allowed to contaminate the ingesta of another, is laid great stress on. The great carelessness on this point in India evidently leads to the preponderance of parasitic diseases in that country, where the heat and attending thirst cause the frequently small supplies of water to be employed for drink when in a very unfit state, or account of the abundance of ova of parasites that it may contain. A description is also given of the manner in which the Burates or Cossacks of the region of Lake Baikal are nearly all infested with tapeworm, from the custom prevalent amongst them of eating their meat-the flesh of calves, sheep, camels, and horses-in an almost raw condition, and in enormous quantities. We think that there is one point in which this work is particularly suggestive. The great gaps there are in our knowledge of helminthology, such as the imperfect information that can be giver to the source of the liver fluke, must cause most readers who have opportunities at their disposal to wish to develop further a subject which has so many obvious practical bearings on the prosperity of this country; for England in the opinion of many competent authorities is developing more and more into a meat-producing and not seed-growing land. The parasites of the sheep, dog, hog, and cat are those which form the rest of this instructive

as

little volume.

Chapters on Trees: a Popular Account of their Nature and Uses. By Mary and Elizabeth Kirby (London: Cassell, Petter, and Galpin.)

The Amateur's Greenhouse and Conservatory. By Shirley Hibberd. (London: Groombridge and Sons, 1873.) WE have here a brace of books on arboriculture and floriculture, each of which will be welcomed by a certain scientific literature. Both are written in an agreeable and class of readers, and will fill a useful place in popular attractive manner, and are bound and generally got up in a style to suit the drawing-room table. The authoress of the first (or authoresses, for though two names appear on the title-page, the pronoun used is sometimes the first person singular) must not be taken too implicitly as a guide in her scientific and structural details. Many of her statements are, to say the least, very doubtful, and bear the marks of a want of acquaintance with the recent results of botanical science. Passing by this defect, we have a great deal of interesting information and gossip about a great number of our forest-trees. There are also very good descriptions, forming the best part of the book, of many other trees of great economic value with which we are not so familiar, as the ebony, the camphor, the nutmegtree, &c. The illustrations-one full-sized one for every tree, besides smaller ones-are, with a few exceptions, excellent.

The second volume, like all Mr. Shirley Hibberd's, contains a great amount of practically useful information on the culture of plants. Indeed anyone who is interested in the matter will find here advice on almost every point connected with the construction and management of plant-houses, and with the selection, cultivation, and improvement of ornamental greenhouse and conservatory plants. There are a large number of woodcuts and some well-executed coloured plates. The book comes, however, more within the range of the gardener than of the scientific student.

Tenth Annual Report of the Belfast Naturalists Field Club. (Belfast: 1873.)

WE are glad to see from the Committee's report that the condition of this club is in every respect satisfactory, both as to numbers, finances, and, most important of all, amount and value of work done by the members. The

first part of the Report is concerned with the six summer excursions of the club in 1872, interesting accounts of the history, antiquities, and natural history of the various places visited being given. Of the papers contained in the volume, we mention the following:-" The Lignite of Antrim and their Relation to the True Coal," by Mr. William Gray, in which the author considers the subject both geologically and economically. The Rev. Dr. MacIlwaine, in a paper on "Life," gives an account of the various theories as to the nature of life held by philosophers from the earliest times to the present day. A different aspect of the same subject is discussed in Mr. Robert Smith's paper on "Darwinism," in which the author briefly sketches the nature of the Darwinian theory of development, and gives practical exemplifications of its working in every-day life. Mr. William Gray gives an entertaining account of some of the doings of the notorious "Flint Jack" in Ireland; and the longest paper in the volume, by the Rev. Edmund M'Clure, is one of considerable ethnological value, on "Family Names as indicative of the Distribution of Races in Ireland." The Society offers a considerable number of prizes, competition for which will no doubt tend to encourage the practical study of the various subjects with which the Society is concerned. Altogether it seems to be in a thoroughly healthy condition.

LETTERS TO THE EDITOR

[The Editor does not hold himself responsible for opinions expressed by his correspondents. No notice is taken of anonymous communications.]

tending for the validity of his Rallus modestus, as distinct from R. dieffenbachii.

The next number of the Ibis will contain my reply to Captain Hutton's communication. In the meantime I will merely state that the whole of his argument rests on the assumption that Rallus dieffenbachii and R. philippensis are the same, in which he is entirely mistaken.

It is a fallacy, therefore, to suppose that because he has shown his bird to be distinct from Rallus philippensis, with which he bachii, which, by his own admission, he has never seen. compares it, he has proved it to be distinct from Rallus dieffenWALTER L. BULLER

Oct. 18

Flight of Birds

IN NATURE, vol. viii. p. 86, Mr. J. Guthrie calls attention to, and asks explanation of, a curious phenomenon in the flight of birds observed by him :-"In the face of a strong wind," he says, "the hawk remained fixed in space without fluttering a its position a few feet with a slight motion of its wings, and then wing for at least two minutes. After a time it quietly changed rocks around it." came to rest again as before, remaining as motionless as the

I have often observed the same phenomenon, but, until recently, not carefully enough to warrant any attempt at explanation, though always convinced that it was not due to any invisible vibratory motion of the wings, as suggested by Mr. Guthrie. During the past summer, however, while on a tour through the mountains of Oregon. I had a fine opportunity of watching very closely a large red-tailed hawk (Buteo montanus) while performing this wonderful feat, and of noting the conditions under which alone, I believe, it is possible. These conditions are precisely those described by Mr. Guthrie, viz., a steady wind, blowing across an upward slope, terminated by a ridge. For a half-hour I watched the hawk, with wings and tail widely expanded, but

Chromosphere.

I HAVE been asked by Prof. Young, of Dartmouth College (U.S.) to say, with reference to the statement made on p. 244 of the third edition of my "Spectrum Analysis" concerning the presence of Ruthenium (Ru) in the solar atmosphere, that possibly by a lapsus calami he may have written the symbol (Rb) when giving the information of his discovery to Dr. Huggins, from whom I received a note on the subject.

Although, in accordance with Prof. Young's desire, I make these remarks, I cannot help feeling that they are quite unnecessary, as no one who knows the careful exactitude of Prof. Young's work could for a moment suppose that he was capable of making a confusion between Rubidium and Ruthenium. H. E. RoscOE

Owens College, Manchester, Nov. 4

The Miller Casella Thermometer

I WAS surprised on reading Messrs. Negretti and Zambra's letter published in your journal of October 23.

I was under the impression that it had been conclusively established that the principle upon which the Casella-Miller or Miller-Casella Deep-Sea Thermometer is constructed is identical with the one originally made in 1857 by Messrs. Negretti and Zambra at the suggestion of Mr. Glaisher, F.R.S., by the late Admiral Fitz-Roy's directions for the Board of Trade.

I was present when Mr. Scott, F.R.S., Director of the Meteorological Department of the Board of Trade, read a paper upon the subject at the Meteorological Society, January 17, 1872; he said:-"I submitted one of these instruments, made for the late Admiral Fitz-Roy, to hydraulic pressure; it proved good and trustworthy. The history of these instruments was perfectly familiar to many gentlemen interested in deep-sea soundings in 1869."

I may add that I saw the original instrument at the Hydrographic Office ten years ago; in justice I am bound to say that Messrs. Negretti and Zambra were the first manufacturers of a deep-sea thermometer unaffected by pressure. 208, Piccadilly, Oct. 29 P. PASTORELLI

Captain Hutton's "Rallus Modestus"

IN the notice of the current Ibis, which appeared in Vol. viii. P. 519, reference is made to a paper by Captain Hutton, con

minutes in the face of a strong wind; then changing his position the ridge. and again balancing, but always choosing his position just above

I explain the phenomenon as follows :-The slope of the hill clines the plane of his expanded wings and tail very slightly determines a slight upward direction to the wind. The bird indownwards, but the inclination is less than that of the wind. Under these conditions it is evident that the tendency of gravity would be to carry the bird forward and downward, while the wind would carry him backward and upward. The bird skilfully adjusts the plane of his wings and tail, so that these two position from time to time, not entirely voluntarily, but because opposing forces shall exactly balance. He changes his place and the varying force or direction of the wind compels him to seek a new position of equilibrium. JOSEPH LE CONTE

Oakland, Cal., U.S., Sept. 19

Collective Instinct

In response to the appeal which closes Mr. Buck's interesting letter (NATURE, vol. viii. p. 332), the following instance of "collective instinct" exhibited by an animal closely allied to the wolf, viz., the Indian jackal, deserves to be recorded. It was communicated to me by a gentleman (since deceased) on whose veracity I can depend. This gentleman was waiting in a tree to shoot tigers as they came to drink at a large lake (I forget the district) skirted by a dense jungle, when about midnight, a large Axis deer emerged from the latter, and went to the water's edge. Then it stopped and sniffed the air in the direction of the jungle, as if suspecting the presence of an enemy; apparently satisfied, however, it began to drink, and continued to do so for a most inordinate length of time. When literally swollen with water it turned to go into the jungle, but was met upon its extreme margin by a jackal, which, with a sharp yelp, turned it again into the open. The deer seemed much startled, and ran along the shore for some distance, when it again attempted to enter the jungle, but was again met and driven back in the same manner. The night being calm, my friend could hear this process being repeated time after time-the yelps becoming successively fainter and fainter in the distance, until they became wholly inaudible. The stratagem thus employed was sufficiently evident. The lake having a long narrow shore intervening between it and the jungle, the jackals formed themselves in line along it, while concealed within the extreme edge of the cover;

and waited until the deer was water-logged. Their prey being thus rendered heavy and short-winded, would fall an easy victim if induced to run sufficiently far,-i.e. if prevented from entering the jungle. It was, of course, impossible to estimate the number of jackals engaged in this hunt, for it is not unlikely that, as soon as one had done duty at one place, it outran the deer to await it in the another.

A native servant, who accompanied my friend, told him that this was a stratagem habitually employed by the jackals in that place, and that they hunted in sufficient numbers "to leave nothing but the bones." As it is a stratagem which could only be effectual under the peculiar local conditions described, it must appear that this example of collective instinct is due to "separate expression," and not to "inherited habit."

Cases of collective instinct are not of infrequent occurrence among dogs. For the accuracy of the two following I can vouch. A small skye and a large mongrel were in the habit of hunting hares and rabbits upon their own account, the small dog having a good nose and the large one great fleetness. These qualities they combined in the most advantageous manner, the terrier driving the game from the cover towards his fleet-footed companion, which was waiting for it outside.

The second case is remarkable for a display of sly sagacity. A friend of mine in this neighbourhood had a small terrier and a large Newfoundland. One day a shepherd called upon him to say that his dogs had been seen worrying sheep the night before. The gentleman said there must be some mistake, as the Newfoundland had not been unchained. A few days afterwards the shepherd again called with the same complaint, vehemently asserting that he was positive as to the identity of the dogs. Consequently, the owner set one watch upon the kennel, and another outside the sheep-enclosure, directing them (in consequence of what the shepherd had told him) not to interfere with the action of the dogs. After this had been done for several nights in succession, the small dog was observed to come at daydawn to the place where the large one was chained: the latter immediately slipped his collar, and the two animals made straight for the sheep. Upon arriving at the enclosure the Newfoundland concealed himself behind a hedge, while the terrier drove the sheep towards his ambush, and the fate of one of them was quickly scaled. When their breakfast was finished the dogs returned home, and the large one, thrusting his head into his collar, lay down again as though nothing had happened. Why this animal should have chosen to hunt by stratagem prey which it could easily have run down, I cannot suggest; but there can be little doubt that so wise a dog must have had some good

IN your number of August 14 (Vol. viii. p. 302) Mr. E. C. Buck alluded to the curious and interesting instances of instinct and gregarious action in lower animals, and mentioned that this action has been more particularly observed in the case of wolves in India. These remarks remind me of a curious instance of combined action between two foxes for the capture of their prey, which I witnessed myself more than once; and as similar proceedings, on the part of these animals have been so frequently observed in the hilly country of the department in which I reside, I cannot but conclude that the same habit will prevail among them, wherever they are found. The case is as follows:-One of the two foxes, in the pursuit of a rabbit or hare, continued yelping at short and regular intervals and thus drove the unsuspecting victim in the direction of the appointed bush, where the other fox was concealed and ready to seize its prey as soon as it came within its reach. The capture being effected, they generally divide the prey between them; but if the ambushed fox, in jumping at its prey, has not gained the end in view, the two baffled compeers alternately repeat many times the unsuccessful leap, in order probably to find out the cause of the miscarriage.

On one

The above allusion to foxes leads me to mention another instance of the ingenuity of these animals, which is very remarkable, and one, I believe, which is but little known. occasion, in early life, when I happened to pass my College vacation at the Chapelle d'Angillon (Department of the Cher), my attention was attracte l twice or three times, when rambling by the side of a small stream called the Petite-Saudre, by a floating mass of moss, which, when drawn to the bank, was found to be swarming with fleas. An old peasant of the neighbourhood, who observed my surprise, gave me the following explanation of the fact, the correctness of which, said he, he could

warrant :-Foxes are much tormented with fleas, and when the infliction becomes severe, they gather, from the bark of trees, moss which they carry in their mouths to the side of a stream where the water deepens by degrees. Here, they enter the water, still carrying the moss in their mouths; and, going backwards beginning from the end of their tail, they advance by slow degrees, till the whole body of the animal, with the exception of the mouth, is entirely immersed. The fleas, during this proceeding, have rushed successively in rapid haste to the dry parts and finally to the moss, and the fox, when he has, according to his calculation, allowed sufficient time for all the fleas to take their departure, quietly opens his mouth. The floating moss, with its interesting freight, is carried away by the stream, and the animal finds its way back to the bank, with an evident feeling of much self-satisfaction at having thus freed himself from his tormentors.

Many persons, and very trustworthy ones, confirmed to me the old peasant's account. Montpellier, Oct. 17 A. PALADILHE

Venomous Caterpillars

ONCE before I wrote to you on this subject, and had hoped that the entomological mountain had long since been safely delivered of its mouse. But from recent communications such ap pears not to be the case.

Any large caterpillar with tolerably stiff hairs that will not, in different degrees, affect tender skin when brought incautiously in contact, may probably be looked upon as a phenomenon. That any larva with stiff spines will occasion inconvenience by more violent contact is, I should think, evident to any thinking naturalist. That inflammatory symptoms will most probably follow in either case is also evident. The puncture made by a single steel filament would occasion little or no inconvenience; but if multitudes of these filaments were simultaneously directed on a limited surface of skin, the result would be very different. The best analogue of the irritation caused by larval hairs is, as I before hinted, to be found in that following the handling of certain boraginaceous plants-Echium vulgare, Symphytum officinale, &c.

Mr. Riley, the State Entomologist for Missouri, has, in his fifth annual report, devoted a chapter to this subject, and states that he is acquainted with fifteen indigenous larvæ having socalled urticating powers, and in every instance the action is mechanical. Those observers who place so much stress upon the fact of contact with a hairy larva causing pain should not let surprise get the better of their judgment; nor, in the case of those residing abroad, should they allow themselves to be influenced by native superstitions. The position is simply this: any hairy larva is likely to cause irritation mechanically, from particles of the numerous hairs piercing the skin; no case has yet been proved in which such irritation is the result of venom, such as that of Urtica among plants. Lewisham, Oct. 10

Harmonic Echoes

R. MCLACHLAN

THE phenomenon mentioned by W. G. M. of notes higher in pitch than the sound producing them being reflected from railings, is not at all uncommon, and is very easy of explanation. Suppose a person standing close to a line of upright bars, the distance between the bars being. a. If he now makes any sharp sound, so as to propagate a single wave, this wave will be successively reflected by each of the bars; sɔ that, in answer to the single wave he propagates, he will have an echo of the pitch corresponding to vibrations per second (V being the velocity of sound). If, however, he stands at any distance, say, from the row of bars, he ought to get a slightly descending echo, as then each wave succeeds the list at a distance increased by twice the difference between √x2 + m2 a2 and V2 + (n-1)2 a2, where n is the number of the bar measured from opposite the observer.

Brampford Speke, Oct. 13

V

2 a

ARNULPH MALLOCK

Evolution as applied to the Chemical Elements WHEN so little is really known about evolution, even in the sphere of organic matter, where this grand principle was first

prominently brought before our notice, it may perhaps seem premature to pursue its action further back in the history of the universe. However, it seems but natural that we should apply this hypothesis to explain the close connection that holds between certain of the so-called elements. Pre-supposing that this theory has not been discussed before, I will just mention the chief grounds for holding it, and leave the examination into its truth or falsity in the hands of more experienced chemists. Herbert Spencer defines evolution as the integration of matter at the expense of force; this integration being accompanied by a loss of polarity, and by specialisation in a certain direction. Thus much being granted let us see how far this change from simple to complex is traceable in the qualities of certain of the elements, as seen especially in those that fall under natural groups.

In the first place, we may call some of the metals more generalised than others. Thus all hydrogen salts are soluble in water; so, to a less extent, are those of lithium, sodium, and potassium; but as the atomic weight (or mass) increases, so the salts of those metals become less and less soluble. This is only true speaking generally, for we see that, in particular cases, the hydrate of barium is more soluble in water than that of calcium, &c. But, as a rule, the salts of barium are less soluble than those of strontium; these, again, than calcium salts. But, on the whole, we may say that with increase of atomic mass of the metals, their salts lose their general properties and become more and more specialised, the salts taking their character from the metal in combination.

Secondly, according to this hypothesis, increase of atomic mass should be accompanied by absorption of motion. Just as the very complex molecules, of which living organisms are built up, are deficient in polarising or crystallising force, so are also the more massive chemical atoms: for it is evident that the heavy atoms of lead and bismuth have far less of this force, called chemical affinity, than have the light sodium, or the still lighter hydrogen atoms. In colloid bodies, the atomic attractions are mostly used up in keeping together the comparatively great masses of the molecule hence but little polarity, or attraction among the molecules themselves, is manifested, and the compounds from the union of these molecules are unstable. So, too, the more massive atoms of elements enter with more difficulty into combination, and the products formed are unstable. Thus, the chlorides of platinum, or the oxides of lead, &c., are less stable, and more difficult of formation, than the corresponding salts of potassium or magnesium. Whereas colloids and crystalloids readily unite together: this is paralleled by the strong affinity that hydrogen, or any metal, has for chlorine or oxygen. Here the metal is the light crystalloid, the non-metal, the colloid, so to speak. It is only with the more specialised of the metals, those which we have seen have massive atoms, that hydrogen will unite, viz., antimony and arsenic; and the compound it forms with the former is very unstable, whilst the hydride of bismuth is unknown. These compounds are not alloys like that of hydrogen with palladium, but they show the comparatively non-metallic nature of arsenic and antimony. This consideration leads us to suppose that the non-metals are still more highly evolved than the metals, and that in the special direction towards electro-negative polarity. Besides we know that the intermediate links differ in degree, not in kind.

The lessening of the atomic heat with increase of mass shows a further absorption of motion, besides the potential energy possessed by the more massive atoms. It might be objected that motion has never been extracted from these massive atoms; on the contrary, as a rule, the heat of combustion is greater as atoms of the element entering into combustion are lighter. But the molecules of organic matter must be decomposed by suitable means before they can do any work; just so with the elements, which receive their name for the very reason that, as far as we know, they are incapable of decomposition. Perhaps, indeed, the increase in the number of rays in the spectra of highly heated sulphur and nitrogen will be regarded as an instance of such motion.

Thirdly, if we look at the atomic weight of groups of the elements, it is seen that the increase of mass occurs by a simple proportion. Gladstone, Dumas, Odling and others have shown the close relation of the numbers for particular groups; whilst lately Mendelejeff has given out a law of periodical recurrence, connecting the properties and the atomic weight, either received or theoretical, of all known elementary bodies. Thus we have

These instances suffice to show how near the calculated ato nic weights come to those found by experiment.

In the fourth place it is a significant fact, that the elements themselves become changed in properties under different circumstances; the allotropic forms that result may be said to correspond with "varieties " among organised bodies. In the case of the elements greater atomic mass was said to denote evolution; in the best known allotropic varieties we find change from the normal form to be accompanied by increased density. Thus ozone (allotropic oxygen) and red phosphorus have both a greater density than the usual forms of these bodies.

With greater evolution, the so-called elements become more electro-negative; so in these instances, ozone has a greater affinity for hydrogen and the metals than has oxygen, and amorphous phosphorus less affinity for oxygen than ordinary phosphorus.

The varieties of sulphur would seem to be exceptions, for they are of less density than the usual form; the specific gravity of crystallised sulphur is 2'05, that of plastic sulphur, 195. However Berthellot terms the crystallised octagonal variety, electronegative, plastic sulphur, on the contrary, electro-positive. Hence the octagonal form is at once denser and more electro-negative, and should be regarded accordingly as more highly evolved.

In the fifth place, let us note some of the actions and reactions of matter and forces.

(a) Heat: In any organic group, generally speaking, the greater the vapour density, accompanying greater complexity, the higher is the boiling point. So it is with the elements, taken according to natural groups, the greater the atomic weight, the higher the fusing or boiling point. This is seen in the case of chlorine, bromine, and iodine; arsenic, antimony, and bismuth, &c. Exceptions to this rule are the three closely allied metals, zinc, cadmium, and mercury, the most volatile of which is the heaviest, the least volatile, the lightest. Again, the more complex the chemical constitution of bodies is, the worse, generally, do they conduct heat and electricity: so too the more highly evolved and massive the atoms, the worse conductors are they as a rule. This applies strictly only to groups, as calcium conducts better than barium or strontium, but silver, though heavier and of greater atomic weight, nearly five times better than calcium. The difference of conducting power between metals and non-metals is very apparent. Where the atomic mass is greater, as the body verges more towards the electro-negative, this loss of conductibility and the high fusing point is easily accounted for by the mechanics of motion. The heavier atom takes longer to communicate its motion in the one case; or is more difficult to move in the other.

Some natural groups of the elements offer good examples of what has just been stated, e.g.