10.000

globule in originating combinations. To the optician it is as needful as the callipers and straight-edge to the engine-fitter-every glass is separately tested by it. Its familiar readings show whether the work is going on right or wrong; by the indications of inward or outward coma whether the oblique pencils are correct, and finally, the least chromatic or spherical error can be ascertained by its means. It may be 'well-known to mathematicians that these globules are not perfectly spherical' (and mathematicians will be correct in all things), but setting aside the fact that the more minute the particle the nearer it approaches to a true sphere, it happens that shape is not of the smallest consequence, or whether it is illuminated by oblique light, for it is not the globule but the absolute point of light reflected from it that is used. The diameter of a mercury globule for correcting the highest powers from a upwards is only the one five-thousandth part of an inch. Perhaps some one who thinks it may advance the subject, will be good enough to calculate the size of the image of a small lamp-flame set at 4 inches distance, reflected from the surface of a convex mirror of 1.300 of an inch radius. Dr. Pigott, by converting the microscope object-glass into a species of telescope, and viewing distant and minute discs of light, professes by means of the 'Aplanatic Searcher' !!! to have discovered spherical error in all our best glasses, to the existence of which everyone else has hitherto been blind. Doubtless a very imposing or 'striking' demonstration may be made out of this, but it is easy to demonstrate that by so doing we are setting at naught the very qualities and advantages of large angular pencils. The conjugate foci are now so far distant, that large angular aperture no longer exists. A difference in the adjusting collar that would produce an enormous amount of spherical aberration, when the object-glass is tried on the globule test, or in its legitimate use as a microscope lens, is scarcely perceptible in the telescope arrangement, and though a badly-corrected glass may not form an image, yet I have no hesitation in affirming that a lens may be made to give perfect definition under the latter condition, that will prove utterly worthless as an objective for the microscope."-Monthly Microscopical Journal, July.

PHYSICS.

The Construction of Thermopiles.-In a recent number of the Transactions of the Royal Society Lord Rosse gives a paper on the construction of thermopiles, which, though we cannot abstract at any very great length, is of considerable importance. Alluding to his experiments, Lord Rosse says that, although the above experiments are far less complete than he could have wished, they are sufficient to show that the sensibility of thermopiles may be considerably increased by diminution of the section of the bars composing them; whether they may be with advantage reduced to a greater extent than he has already done he cannot say, but he is inclined to think that they may. He has ascertained from Messrs. Elliott that the alloys used by them in the construction of thermopiles, at the time when he received his from them, were 32 parts of bismuth +1 part of antimony, and 14 of bismuth +1 part of tin. If allowance be made for the substitution

of the first of these two alloys for pure bismuth, the difference between Elliott's pile and the pairs II. & III. will be rather greater. The pile by Messrs. Elliott, if made of the same metals as he employed, would have been reduced in power from 1 to 09. The construction of thermo-couples, on the plan he has described, is comparatively easy. In about two hours he was able to make one, and in more experienced hands their construction would be still easier. An experiment was made with one of the piles to ascertain whether, when the heat was not directed centrally on the pile, much diminution of power would take place. There was less deviation, in consequence of the increase of the mean distance which the heat had to travel before it reached the soldering; but he believes that this defect might be remedied, probably without diminution of the power of the pile, by increasing the thickness of the face, and leaving the dimensions of the bars the same.

Improved Bichromate Battery.-In a letter written to the Journal of the Franklin Institute, Mr. W. Poole Levison, of Cambridge, Massachusetts, says that in the spring of 1869, while making use of a small bichromate of potash battery, he discovered that the addition of nitric acid to the mixture of potassic bichromate and sulphuric acid, contained in its porous cups, conferred upon it the virtue of steadiness, without involving the evolution of annoying fumes. For over two months, during last summer, he had in almost constant action a combination of twenty-three large Bunsen cells charged with dilute sulphuric acid and the triple mixture mentioned, and "set up" openly upon the floor of his room. Not only did he work about it with perfect comfort, but left choice brass instruments in its immediate neighbourhood with impunity. Its energy never fluctuated, but after remaining for some time steady, declined, precisely as if the electro-negative plates were bathed in nitric acid only. To a cooled mixture of potassic bichromate solution and sulphuric acid (perhaps preferably in atomic proportions) add nitric acid. The proportion of nitric acid may be greatly varied, as its office is merely to transfer oxygen.

Opening of the Kepler Monument.—The following very interesting account of this is taken from Les Mondes (July 14). On the 24th of last June, the very small Swabian town named Weildiestadt, with hardly 2,000 inhabitants, was the scene of a festive gathering for the purpose of unveiling the statue of the celebrated Kepler, who was born in an humble cottage yet existing, and now known as Kylerhaus. The statue of the celebrated astronomer, executed in bronze, represents him seated on an arm-chair; in bis left hand, supported by a celestial globe, he holds a scroll, upon which an ellipse is delineated; in his right hand he holds a pair of opened compasses. At the four corners of the pedestal, upon which the statue is placed, are smaller statues, representing Michel Mastin, the Tübingen professor who taught Kepler mathematics, and Nicholas Copernicus, Tycho Brahe, and Jobst Byrg, who assisted Kepler in making astronomical instruments. On the centre of the pedestal is simply placed "Kepler; " the other sides of this portion of the monument are embellished with bas-relief representations of incidents of Kepler's life.

The Effect of Artificial Light on the Eyes.-The Chemical News takes the following interesting paper from Les Mondes. It is by M. V. Meunier. The

author states that the great difference between sun and artificial light is due to the fact that, of the light emitted from the former, about half the quantity of rays are luminous and calorific at the same time; but, as regards our artificial light, for ordinary oil (colza oil), the amount of non-luminous, yet calorific, rays is 90 per cent.; for white-hot platinum, 98 per cent. ; alcohol flame, 99 per cent.; electric light, 80, and gas-light, 90 per cent.; while for petroleum and paraffin oils, the amount is 94 per cent. It is this large quantity of caloric rays in artificial light which causes the fatigue to the eyes; but this inconvenience may, according to the author, be almost entirely obviated by intercepting the thermic rays by glass, or, better yet, mica plates. The use of these renders the light soft and agreeable to the

eyes.

The Exact Comparison of Measures of Length.-It would seem from the second publication so long after the first one, that this paper is considered of importance. Illustrated with several engravings it was originally written and published by Herr. F. J. Stamkart, in Dutch, as far back as the year 1839, but is here (Chemical News) reproduced in French at the suggestion of Professor F. Kaiser, partly in order to prove to M. Steinheil, of Munich, that the author (M. Stamkart) had, some thirty years ago, already invented what the German savant has lately described under the name of fühlspiegel, and chiefly because M. Stamkart's invention is of the highest importance just now for the purpose of aiding the exact reproduction of the standards of length (étalon prototype) of the mètre.

Oxygen in Petroleum Wells.—It is stated by M. Widemann, who is connected with the works of the New York Oxygen Gas Company, that the use of oxygen in renewing and increasing the flow of oil in petroleum wells has been so successful that a regular trade has sprung up in oxygen gas for this purpose. The gas is injected into the wells through tubes, and, mingling with the hydrocarbon vapours, forms an explosive mixture, which, when ignited, completely opens seams which have become clogged, and thus renews the flow.-Scientific American.

Temperature of Last Winter in Europe. The recent experiments of Dr. Dove lead him to believe that abnormally low temperatures travel from East to West and abnormally high temperatures from West to East. He has proved this by various experiments during the past winter.

Loss of a Distinguished Physicist.-The town of Mulhouse has just lost a very celebrated citizen, brother of the celebrated manufacturer, M. J. Dollfus. The deceased had left the pursuits of industry to devote his time entirely to science, and especially to geology and mineralogy. He was one of the most expert explorers of Alpine glaciers, and his extensive researches in science associate his name with those of Agassiz, Des Desor, and Des Martius. The deceased was a man of great wealth, and was highly respected by all who were acquainted with him.

Further Researches on Cotton Respirators.—Dr. Jouglet has been experimenting on the use of cotton respirators, and states that, by their application, the disease known as miner's anæmia, and also the dangers of the effects of lead, copper, and mercury, to those who have to handle these metals, or work in vapours or dust thereof, may be prevented.-Vide Comptesrendus, August.

Ice Machine for Brewers.-MM. L. Martin and Vindhaussen have given lengthy and full descriptions of two apparatus based upon the principle that, if the expansion of a gas (atmospheric air in this instance) is effected by mechanical means, absorption of heat-in other words, production of cold—– takes place. The ice-making machine produces 100 kilos. of ice at a cost of about sixpence. The cooling apparatus is so arranged as to effect a drying of the malt and cool the wort at the same time.-Revue hebdomadaire de Chimie.

The Emission of Heat.-Herr G. Magnus continues his observations on this point. The last instalment of this lengthy memoir is divided into the following sections :-On reflection of heat; description of experiments; reflection from the surface of other substances than silver, glass, rock-salt, and sylvine; reflection under various angles; results.-Ann. der Physik, No. 4. Galvanic Element with one Liquid.--A description of such an apparatus is given in the Revue hebdomadaire de Chimie (July 14). It is a galvanic cell composed of zinc and carbon placed in a fluid made up of 40 parts of water, 4.5 parts of bichromate of potassa, 9 parts of concentrated sulphuric acid, 4 parts of sulphate of soda, and 4 parts of the double sulphate of potassa and iron. This element produces a very regular current. The zinc need not be amalgamated, and no gas is evolved.

A Straight-needled Galvanometer.-A description, illustrated by woodcuts, appears in the Revue hebdomadaire de Chimie by M. Bourbouze. The object of the inventor is to render slight deviations visible to a large number of students simultaneously.

Underground Temperature.-From observations that have been carried on from 1864 to 1870 by MM. A. C. Becquerel and E. Becquerel, it seems that at 36 mètres below the surface the temperature is constantly 12-47°, and that at a depth of from 36 to 26 mètres a very slight difference only is observed. The paper contains a lengthened series of tabulated results.— Comptes-rendus, July 18.

Contribution to Terrestrial Magnetism.—We learn from the Proceedings of the Royal Society that a valuable paper on the above has been sent in by General Sir Edward Sabine, K.C.B., the President. It is accompanied by maps of the declination, inclination, and magnetic force, which have been drawn at the Hydrographic Office of the Admiralty under the superintendence of Captain Frederick John Evans, R.N., F.R.S. The paper consists in great measure of Tables, giving the observation of each of the three magnetic elements, with reductions in every case for the secular change between the date of the observation and that of the epoch (1842-5) for which the maps are constructed.

ZOOLOGY AND COMPARATIVE ANATOMY.

Eyes in the Mole.—The mole is blind. Not so the fœtal mole, which Mr. R. I. Lee, in a paper read before the Royal Society (April 28), proves: Mr. Lee's paper is not very fully published in the Proceedings; but such as it is, it contains much information. It concludes as follows:-It must necessarily happen that many interesting observations are made in the course of

an investigation like that which has been briefly described, and many minute details might have been added to this account; but it appeared to me to be desirable to limit the details, as far as possible, to those which were sufficient to establish the remarkable physiological fact that the mole, at the time of birth, is endowed with organs of vision of considerable perfection, while in mature age it is deprived of the means of sight in consequence of certain changes which take place in the base of the skull, terminating in the destruction of the most important structures on which the enjoyment of the sense of sight depends.

The Measurement of Teeth.-In a paper laid before the Royal Society in May last, Mr. Busk gave some very important advice relative to the method of giving the measurement of teeth. He says that the respective measurements, which may be taken with a pair of sharp-pointed calipercompasses, having been pricked out upon the equidistant horizontal lines, the points showing the length and breadth of each tooth are connected by straight lines, and a sort of figure is thus obtained which, in nearly all cases, will be characteristic of the genus or family, and in many instances sufficient to determine the species also. In some cases, as for instance in Canis and Viverra, the odontograms are at first sight so nearly alike that recourse must be had to the pattern of the teeth in addition, as before alluded to. In order to render figures of this kind easily comparable inter se, it is necessary that they should be drawn upon some common scale for the distance between the horizontal lines. This is, of course, entirely arbitrary, all that is requisite being that it should not be too great nor too small.

The Growth of Shells.-The Proceedings of the Royal Society (June 16) contain a very interesting paper by Professor L. Macalister on this subject. He says that while engaged in arranging the large collection of shells in the Museum of the University of Dublin, he was led to mak measurements of univalve shells in order to see whether any deduction o zoological importance might be drawn from these valuable geometrical observations, and more especially to determine whether it might be possible to arrive at constant specific numerical parameters in these cases; and in all instances he has been surprised by finding that, in well-formed shells, the ratios of the successive whorls have been specifically constant. In making these measurements, the points to be determined are three, viz.:-1st, the ratio of elongation of the radius vector of the spiral; 2nd, the degree of linear expansion of the generating figure in the successive whorls; and 3rd, the degree of translation or slipping of the spiral on the central axis. The second of these we may call the discoidal coefficient, and the third the helicoidal coefficient.

The Lower Races of Man.-Sir John Lubbock delivered an interesting address on this subject at Liverpool. Among the extraordinary points were those concerning marriage. Thus, the idea of marriage does not in fact exist in the Sandwich Island system of relationship. Uncleships, auntships, cousinships, are ignored, and we have only grandparents, parents, brothers and sisters, children, and grandchildren. Here it is clear that the child is related to the group. It is not specially related either to its father or its mother, who stand in the same relation as more uncles and aunts, so that every child has several fathers and several mothers.