temperature a tension of dissociation which is measured by the elastic force of the aqueous vapour which it emits at this temperature. Applying this to the explanation of the phenomena of hydration and efflorescence, he states further that a salt becomes hydrated when the tension of the aqueous vapour contained in the atmosphere is greater than that which the salt emits at the same temperature. Efflorescence results when the tension of the watervapour of the salt is greater than that of the aqueous vapour existing in the atmosphere. Hydrous salts which do not effloresce owe, then, this property to the inferior tension of aqueous vapour emitted by them at common temperatures to that ordinarily possessed by the aqueous vapour in the atmosphere. These identical salts effloresce when placed in an atmosphere where the elastic force of the aqueous vapour contained in the air is below that which they emit.

Professor Knoblauch has made an investigation on the interference-colours of radiant heat. Some of his results are embodied in the following:-When two groups of rays meet under certain conditions, radiant heat differs in its properties after the meeting; for instance, as regards its property of traversing diathermanous bodies, it manifests an interference-colour. If this is produced in doubly refracting crystals, under the influence of a polarizing agent, placed for instance between two Nicol's prisms, and the plate of crystal fixed while one prism is rotated, the colour passes through white to the complementary. On rotating the plate of crystal in its plane, when the principal sections of the Nicol's prisms are parallel, only one thermal colour occurs; when they are at right angles, the complementary colour; while when they form an angle of 45°, both thermal colours appear.

Experiments have been made in Germany which tend to show that molten lead dropped upon liquid iron remains floating on the surface of the latter. Since the specific gravity of lead is more than one-half greater than that of cast-iron, the fact seemed anomalous. Professor Karmarsch, of Hanover, has explained the matter very satisfactorily. Some samples of these drops of lead lying embedded in the surface of a cast-iron block were sent to the Professor by an ironmaster. Professor Karmarsch found, upon close examination, that these drops of lead were not solid globules, but hollow, formed apparently as bubbles. According to this explanation, the lead is kept resting on the surface of the iron by its own vapour. In large quantities the result is known to be different, lead being occasionally tapped from the bottom of blast furnaces employed in smelting certain classes of ores.

The value of petroleum as fuel for steamship boilers has been for a considerable time under investigation by the United States

Naval Department. The Secretary has finally reported against petroleum; the only advantage thus far shown is a not very important reduction in bulk and weight of fuel carried.

ELECTRICITY.-H. Poggendorff has published an account of a new electrical phenomenon observed by him. This physicist was experimenting with exhausted tubes containing a certain quantity of mercury, having either at one end or both, platinum wires, when he encountered the phenomenon. More precisely the circumstances under which his first observation was made were the following:A tube of the kind described above, containing only one wire, coated towards both extremities with a broad band of tinfoil, was placed as an exhausted double jar across the electrodes of a Holtz's machine. While the tube lay in this position on the electrodes, there appeared to be a certain motion in the mercury. As this motion could have no definite character, the current in such a jar being an alternating one, another tube was made provided with platinum wires at both ends, and the current passed through the length of the tube, the tube being placed as far as possible horizontally. In this case a more decided motion of the mercury was observed, but still scarcely as decisive as could be desired. A third, fourth, and fifth tube showed the phenomenon in about the same degree. A sixth tube, however, removed all doubt. This had not only been carefully exhausted, but the mercury in it had been kept briskly boiling for some time; the mercury was kept out of contact with the platinum wires by the tube being bent at right angles at about an inch from each end. The tube thus prepared was hung by wire hooks to the electrodes of the machine, in such a manner that the body of it was perfectly horizontal, the mercury serving as a level. As soon as the adjustment was properly made, the machine was set in action. When the current passed through the tube, the mercury rapidly travelled from the negative to the positive pole. However the current was sent, the result was always the same. In experimenting, the mercury was generally made to occupy a thread of about 4 inches in length; the horizontal part of the tube was about a foot in length, so that the thread had to move over a space of 8 inches. Two or three seconds was the time generally occupied by the mercury in travelling from one end to the other. The thread changes shape as soon as it commences to move, becoming considerably longer; the elongation amounted in these experiments to an inch. The quantity of mercury set in motion was one ounce; very small quantities of the metal will not move, probably a result of adhesion.

H. Poggendorff also believes himself entitled to state generally that the electro-negative metals, platinum, gold, palladium, silver, &c., render the following insulators positive by friction, while the

electro-positive metals, zinc, cadmium, iron, &c., induce in these insulators the negative condition-ebonite, gutta-percha, caoutchouc, waxed cloth, white wax, resin, shellac, sealing-wax, sulphur, amber, copal, silk, pyroxyline, collodion, and gun-cotton. There are a few exceptions in the behaviour of the metals. A good example of the general law laid down is furnished by ebonite. Gently rubbed with platinum it becomes positive, zinc or iron inducing the negative condition.

M. H. de Saussure has published a paper in the Bibliothèque Universelle,'" On the Humming Sound produced on Mountains by Electricity." In June, 1865, M. de Saussure and a friend climbed the peak of Piz Surley. When the summit had been reached, sleet fell abundantly; preparatory to taking their repast, they laid the alpenstocks against a little cairn of dry stones. Almost at the same moment, M. de Saussure felt acute pain in one shoulder, speedily in the other also, and in the back. The pain resembled the pricking of pins. Soon the alpenstocks resting against the rock commenced to sing loudly, the sound resembling that emitted by a kettle of water about to boil. Strong currents of electricity flowed from all the salient parts of the body, and the hair stood out. M. de Saussure remarks that in every instance where the phenomenon has been observed, the mountain peak has been enveloped in a shower of frozen sleet.

A new voltaic battery has been devised by Dr. Hugo Müller and Dr. Warren De la Rue. The negative element is chloride of silver fused around a silver wire, which serves as conductor; this wire is bent over and connected by means of a small caoutchouc collar to a rod of zinc, which need not be amalgamated. The exciting liquid is salt water. In course of time the liquid becomes saturated with chloride of zinc; when metallic zinc begins to deposit on the negative plate the battery must be renewed with fresh solution. The tension of a battery of ten cells (the couples being very small, about three inches in height) is sufficiently great to decompose water enough to yield a cubic inch of the mixed gases in about twenty minutes. Dr. De la Rue has constructed a battery of two hundred cells.

M. Bourgoin continues his investigation regarding the electrolysis of organic acids. The current acts on acetate of potassium as on a mineral substance. In a moderately alkaline solution the oxygen reacts on the elements of the anhydrous acid, giving rise to carbonic acid and hydride of ethylen. A certain quantity of acid is totally consumed under the influence of oxygen furnished either by the salt or by the alkaline water. The portions of liquid at the two poles suffer unequal losses; almost the whole is lost at the

positive pole. When the current is made to act on free acetic acid it concentrates the acid at the positive pole. He has also examined the action of the current on neutral tartrate of potash, on a mixture of tartrate and alkali, also on free tartaric acid. With the neutral tartrate, as soon as the current passes, the solution becomes alkaline at the negative pole; the principal result is the formation of a white precipitate at the positive pole. Analysis has shown this substance to be cream of tartar. The gas evolved at the positive pole was found to be composed of carbonic acid, oxygen, carbonic oxide, and nitrogen. When the current acts on a mixture of neutral tartrate and alkali the results are different. The gas evolved at the positive pole is then composed of carbonic acid, carbonic oxide, oxygen, and hydride of ethylen: acetylen has also been detected in it. The decomposition of free tartaric acid yielded the same products as the neutral tartrate, but in different proportions. Acetic acid was formed at the positive pole, and after an experiment had been in progress five days, a considerable quantity was isolated as acetate of baryta.

12. ZOOLOGY-ANIMAL MORPHOLOGY AND

PHYSIOLOGY.

(Proceedings of the Zoological Society of London.)
MORPHOLOGY.

The Size of the Brain in Different Races of Men.-Dr. J. Barnard Davis has communicated a paper on this subject to the Royal Society. There has always been considerable difficulty in getting at a knowledge of the variation of the brain in various races, because it has been thought necessary to examine and weigh the brain itself, and this has not been done in the case of many exotic races. The method of gauging the skull cavity has been said to be of no real value, and hence has not been extensively applied. Dr. Davis shows that this is a mistake, and possibly the method of gauging is more reliable than that of weighing, for thereby the error likely to arise from the shrinking of the brain during fatal disease and from post-mortem changes is avoided. Dry Calais sand is used for gauging the brain-case, and an allowance of 15 per cent. is deducted for other structures present in addition to the brain. This amount has been very carefully estimated from a large series of observations. The sand is then weighed and reduced to its equivalent in cerebral matter of 1,040 specific gravity. Professors Tiedemann and Morton, who have made similar observations to those of Dr. Davis, omitted to make this allowance, and also (a much more important omission) did not discriminate male and female skulls. This led to serious error, since the female brain is

VOL. V.

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on the average 10 per cent. less in weight than the male. As the result of his investigations Dr. Davis gives a long list which is very interesting. He gives as an average 47 oz. for the English brain, 45 oz. for the French; Italians, Lapps, Swedes, and Dutch nearly the same as English. As to the Germans, he has not got a satisfactory result. Hindoos have 44 oz. of brain, the aboriginal Khonds of India only 37 oz., whilst Chinese and Siamese have 47 oz. Of African races, the more northern negroes have from 44 to 46 oz. of brain, whilst in the south we find the greatest contrast of capacity known, for whilst the Bushmen range from 31 to 39 oz. only, the Kafir has on an average over 48 oz., a greater weight of brain than has the average Englishman. The bold and enterprising Malays present a high brain-weight (over 47 oz.), as also do the supposed aboriginal inhabitants of the Western Pacific. Dr. Davis does not state what collection of skulls it is which he has used in making these calculations. From some of his remarks, it is evident that the collection is not a very large one, and thus the value of the results is diminished. Several hundred cases ought to be collated in each race to give a satisfactory result.

Fur-seals and Hair-seals.-Dr. J. E. Gray has been recently writing on these animals, which are not only matters of curiosity to the world at large, on account of their strange forms, and of interest to zoologists especially, but also have a very considerable commercial importance in respect of their skins and their fat. The Eared-seals (Otariadæ) inhabit the colder parts of the southern hemisphere; they are also called "Fur-seals " by the sealers, because they have a soft under-fur between the roots of the longer and more rigid hairs. Some are called "Hair-seals" because they have only rigid hairs, and are not worth making into "seal-skins." These are only hunted for their fat, the skins if used being only applied to common purposes, such as covering boxes, &c., as with the skins of the ordinary Earless-seals. Though zoologists have had great difficulty about distinguishing the various species of Eared-seals, it is not so with the practical dealer in skins; he knows the difference between the various kinds of skin at a glance, just as the dealers in whalebone were in advance of scientific men in distinguishing the species of whale by their baleen. With regard to the Sea-bear which was lately exhibited in the Zoological Gardens in London, Dr. Gray decides that it is the Otaria jubata. There has been great difference of opinion on this point, but Dr. Gray has examined the skull of the animal. He is anxious to see the account of the anatomy of this specimen, which Dr. Murie is to publish. The French sailor, Leconte, who brought this Sea-bear to England from Cape Horn, has been sent by the Zoological Society to the Falkland Islands, for the purpose of procuring some other seals of the southern hemisphere.