pheric pressure; although the percentage difference is not constant. On adding a little free sulphuric acid to the air solution, however, this difference becomes more constant and is higher than before. On adding the acid to both voltameters the percentage difference becomes constant within the limits of experimental error. In this case, where the current density rises above 0:01 ampere per square centimeter of active kathode, there is no practical difference between the two deposits. For densities below this value however the vacuum deposit is appreciably higher than the air deposit. If a curve be drawn to represent the deposits obtained in a vacuum at different current densities, it will be observed to be more regular than the air curve, and to be approximately a straight line for densities below 0:01 ampere per square centimeter. In a paper following this, SCHUSTER gives the details of certain experiments made by him some years ago, proving that when copper is placed in a copper sulphate solution containing free sulphuric acid, and the tubes are exhausted of air, the diminution in the weight of the copper is quite insignificant compared with what takes place in the presence of air. In sulphuric acid alone the metal behaves similarly.-Proc. Roy. Soc., lv, 66, 84, January, 1894. G. F. B. 7. On the Propagation of Electromagnetic Waves in Ice and on the Dielectric Power of this Substance; by M. BLONDLOT.-In a previous note (Comptes Rendus, July 25, 1892) I enunciated the following proposition:-The length of the waves which an electromagnetic oscillation can emit is the same whatever be the insulating medium in which the experiment is made; in other words, the wave-length depends on the oscillator alone, just as in acoustics the wave-length of a pipe depends only on the length of the pipe. The confirmatory experiments described in the Note cited referred to oil of turpentine and to castor oil; the law holds perfectly for both these substances, and everything leads to the belief that this will be the same for other dielectrics. There is, however, a doubt about ice, in consequence of the exceptional properties ascribed to it. The experiments of M. Bouty (Comptes Rendus, March 7, 1892) show in fact that ice has a dielectric power of 27, that is to say incomparably greater than that of all other substances. Suspecting that the law relative to the propagation of waves might not apply to a dielectric so different from the others, 1 resolved to submit the question to experi ment. For these investigations I availed myself of the intense and prolonged frosts of the winter of 1892-93. M. M. Dufour has helped me in carrying them out, which the rigour of the cold rendered difficult and even painful. I thank him for his extreme kindness on this occasion. The method which I adopted was the following, which, with slight modifications necessitated by the solid character of the dielectric, is the same as that I used in the case of turpentine and castor oil. Electromagnetic waves were transmitted along two tinned copper wires 2.5 millim. in diameter stretched horizontally and parallel to each other at a distance of 0.8 meter. A resonator of gilt copper is placed in a fixed position between the wires; the portion of the transmitting wires beyond the resonator is contained in a wooden trough 4 meters in length. The trough being filled with liquid, the position is sought at which a movable bridge must be placed, joining the wires beyond the resonator to cause the spark to disappear; the distance from the bridge to the resonator is then a quarter of the specific wave-length of the resonator; the position of the bridge is accurately noted. That done, I surround the part of the resonator forming the condenser with a water-tight bag of parchment-paper which I fill with distilled water, and then freeze this water; the layer of air is thus replaced by one of ice. Measuring the wave-length afresh, it is found to be considerably greater than in the first experiment, 141 having become of what it was. The trough is then filled with water which is frozen, and then the position of the bridge for disappearance of the spark is again sought. For this purpose the ice at the distant end of the trough is broken and progressively removed. I ascertained that this position is exactly the same as in the first case, when the dielectric was air. The experiment four times repeated, varying each time the capacity of the condenser, always gave the same result. The proposition relative to the wave-length is therefore true for ice as well as for other dielectrics. Hence, as shown in my previous Note, Maxwell's relation that the dielectric power is also equal to the square of the refractive index also holds for electromagnetic waves in the case given. The preceding results, partly unforeseen, led me to determine the dielectric constant of ice, using electromagnetic undulations. The experiment cited above gave all the data necessary for this determination. For if A and A' are the wave-lengths corresponding to a given resonator, working respectively in air and in a substance of dielectric power K, we have The experiment repeated a dozen times always gave the same result. I consider the relative error does not exceed, for the plate of ice was almost entirely free from air bubbles. According to this, ice does not present exceptional dielectric properties. It remains to be explained how MM. Bouty and A. Perot obtained values of a totally different order for the dielectric power of ice. In the first place, in M. Bouty's method the charge and discharge were enormously slower than in my experiments. Is it not probable, then, that the physical magnitudes measured by M. Bouty and myself were in themselves very different. In any case we know at present too little about the dielectric properties of bodies to be surprised at the divergences of numbers obtained by two methods so dissimilar, however great they are.- Comptes Rendus, October 8, 1894.-Phil. Mag., xxxviii, 578, Dec., 1894. 8. Rotation of magnetic lines.-E. LECHER describes in the Wiener Berichte an experiment performed to test whether, when a magnet turns about its magnetic axis, the lines of force remain at rest or turn with the magnet. A magnet was divided by an equatorial plane into two parts which could turn independently. It was possible to obtain from the two extremities of the magnet an induced current of such a magnitude as cannot be explained by the cutting of the rotating lines of force by the extremely short brushes employed. These currents can be explained if we suppose that a rotating magnet cuts its own lines of force which remain fixed in space.-Nature, Nov. 22, 1894, p. 84. J. T. 9. Magnetization of iron and nickel wire.-KLEMENCIC has measured the permeability of iron steel and nickel wire with the rapidly alternating currents employed by Hertz. He employed the method of a thermal junction previously described by him and obtains the following values. -Ann. der Physik und Chemie, No. 12, pp. 705-720. J. T. 10. New Storage Battery.-In researches on the condensation of electrolytic gases by porous bodies, particularly by metals of the platinum group, M. L. CAILLELET and E.. COLLARDEAU find that platinum and palladium in the spongy condition and ruthenium, iridium and gold in the finely divided state form poles. which condense electrolytic gases and hence produce a gas battery, which on connection of the poles is capable of giving up the stored energy for a short period. The storage capacity is vastly increased by subjecting the poles to great pressure during charging. With spongy platinum and iridium a storage capacity can be obtained which is greater than the capacity of lead accumulators per unit of weight. With finely divided palladium, a storage capacity of 176 ampere-hours per kilograms of palladium was obtained at a pressure of 600 atmospheres. The storage capacity of an ordinary lead accumulator is about 15 amperehours per kilogram of lead.- Comptes Rendus, Nov. 12, 1894. J. T. 11. Resemblances between the grouping of figures on soap films and the arrangement of stars and nebula.-In a leading article, Professor QUINCKE, of Heidelberg, draws attention to the remarkable resemblances between the figures produced on oily films by the operation of water, and the grouping of stars and nebulæ. He suggests that the tendency of modern physics is to ignore any qualitative differences between infinitely great and infinitely small distances. The great masses of the fixed stars in infinite space and the little masses of the infinitely near molecules in the soap films must react upon each other according to the same laws. The protoplasm of organic nature also resembles in structure and movement phenomena, the structure and movements observed on oily films. Ann. der Physik und Chemie, No. 12, 1894, pp. 593– 632. J. T. II. GEOLOGY AND MINERALOGY. 1. Glacial succession in Europe.-The following quotations from the third edition of Geikie's The Great Ice Age,* will present to our readers in concise form the latest views of the author upon the glacial succession in Great Britain and Europe, and the chief data upon which the interpretation is based. I. PREGLACIAL TIMES.-The earliest indications of the approaching Ice Age are met with in the marine deposits of the Pliocene system. The older Pliocene deposits introduce us to a time when the waters of the North Sea were tenanted by a fauna which is clearly indicative of genial climatic conditions. And similar testimony to the warmth of the period is furnished by the contemporaneous marine lacustrine and terrestrial accumulations of other regions of Europe. In those days the sea occupied eonsiderable tracts in the east and south of England, in Belgium, Holland, Northern and Western France, and the coast-lands of the Mediterranean. As time rolled on, however, the genial conditions gradually passed away. The southern forms slowly retreated from the North Sea, while at the same time northern and boreal types came to occupy their place. Similar migrations were in progress farther south, many British and boreal forms finding their way into the Mediterranean. Upon the land like changes *The Great Ice Age and its relation to the Antiquity of man; by James Geikie, third edition, largly rewritten, pp. 850. (Edward Stanford). London, 1894. 66 The general reader will quite understand what is meant by the term 'preglacial," but I ought to mention that it has been applied by geologists to certain deposits which underlie the "lower boulder-clay" of the regions in which these deposits occur. But, as we have learned, many accumulations of so-called "lower boulder-clay" are not the products of the earliest epoch of glaciation, and the fossiliferous beds which sometimes underlie them are, therefore, not necessarily of preglacial age. I apply the term exclusively to deposits which were laid down before the earliest appearance of glacial conditions in temperate latitudes. These, so far as our present knowledge goes, are the only accumulations which we are justified in classing as preglacial. were brought about-the luxuriant flora and the great mammals of the Pliocene retreating gradually before the approaching winter of the Glacial Period. II. FIRST GLACIAL EPOCH.-Eventually a thoroughly arctic fauna lived in the North Sea. Great snow-fields at the same time came into existence, and a gigantic glacier occupied the basin of the Baltic.* The mountainous parts of the British Islands, we can hardly doubt, must likewise have been ice-clad, but of this there is no direct evidence. Farther south the Alpine Lands were swathed in snow and ice, and great glaciers occupied all the mountain-valleys and piled up their terminal moraines upon the low-grounds at the foot of the chain. In Central France very considerable glaciers also descended from the great volcanic cones of Auvergne and Cantal, and deployed upon the plateaux. And probably in many other mountain-districts similar conditions obtained. III. FIRST INTERGLACIAL EPOCH.-Eventually cold conditions. passed away. The arctic fauna retreated from the North Sea, and at the same time dry land occupied the southern part of that sea up to the latitude of Norfolk at least. Across this new-born land flowed the Rhine and other rivers. A temperate flora, comparable to that now existing in England, clothed the land in our latitude, while the hippopotamus, elephants, deer, and other mammals became denizens of our country. In other parts of Europe similar genial conditions obtained-conditions which, to judge from the flora, were even more genial than are now experienced in the same regions. A luxuriant deciduous flora occupied the valleys of the Alps, and flourished at heights which it no longer attains. That flora was accompanied by a mammalian fauna (North Italy) which embraced among other forms Elephas meridionalis. From the amount of river-erosion effected during this epoch we may gather that the stage was one of long duration. By-and-by, however, cold conditions again supervened-the temperate flora disappeared from England, and was gradually replaced by arctic forms. IV. SECOND GLACIAL EPOCH.-The appearance of that arctic flora and the immigration into the North Sea of arctic mollusks heralded the approach of the greatest of the European ice-sheets. This enormous mer de glace covered all the northern part of the Continent and flowed south into Saxony. At the same time the Alpine glaciers reached their greatest extension, while in all the other mountains of Europe snow-fields and glaciers made their appearance. In extraglacial tracts, as in Southern England and Northern France, and in many other regions, the formation of rock-rubble was in active progress, and much movement of such superficial accumulations took place. These physical changes The limits reached by this earliest "great Baltic glacier" are not known. In Southern Sweden, however, it occupied a wider area than the great Baltic glacier of the fourth glacial epoch, its northern limits lying at least thirty miles farther north than those reached by the latter. |