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Among physical researches we may call attention to some interesting observations recently recorded by M. E. Becquerel. It is well known that, in addition to the bright rainbow-tinted band which we observe when a beam of solar light is decomposed by a prism into its constituent coloured rays, there are also present at both ends of the spectrum other rays which entirely elude observation

by the eye. Neither the violet rays, which form the visible limit at

one end, nor the red rays, which form a similar limit at the other, represent the true extremity of the spectrum. The highly refrangible rays beyond the violet end, so potent in their chemical effects, may by certain means be rendered visible; and M. Becquerel has recently shown us how to observe the ultra-red region, or those rays which lie outside the visible spectrum at its less refrangible end, and which are generally known only by their calorific effects. When certain phosphorescent substances have become luminous by the action of the violet or ultra-violet rays, this luminosity may be destroyed, wholly or partially, by exposure to the ultra-red rays. Taking advantage of this fact, M. Becquerel proceeds as follows:-Two parallel beams of solar light are thrown on to two prisms. One of these is of bisulphide of carbon, and projects its spectrum on to a phosphorescent substance, preferably hexagonal zinc-blende. The second prism, which is of flint-glass, is so adjusted that only, the ultra-violet part of its spectrum is allowed to fall on the blende. It is then seen that in the ultra-red part of the first spectrum the phosphorescence excited by the ultra-violet part of the second spectrum is partially destroyed, but not uniformly, so that alternating dark and light bands are exhibited. Here, then, we have an entirely new method of studying the region outside the red end of the spectrum. It has been found by this means that the active part of the spectrum extends beyond the red to a distance. more than equal to that between the lines A and D in the visible spectrum.

There is perhaps a tendency among men of science to value rather too slightly the constructive skill of the philosophicalinstrument maker. The grand collection of scientific apparatus recently got together at South Kensington strikingly reminded us of the perfection to which this art has attained, and the material aid which it thus renders to science. An induction-coil of extraordinary magnitude and power has recently been constructed for Mr. Spottiswoode, who has published a description of it in the Philosophical

Sur l'Observation de la partie infra-rouge du spectre solaire, au moyen des effets de Phosphorescence.' Par M. Edmond Becquerel. Annales de Chimie et de Physique, January 1877, p. 5. Also Beiblätter to Poggendorff's Annalen, No. 1, 1877, p. 55.

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Magazine, remarking, with characteristic generosity, that its construction is an instrumental feat deserving of record in the annals of science. Since the time when Ruhmkorff devised his powerful inductorium, coils of this kind have become so popular that the smaller ones are almost household toys, and consequently their construction is tolerably well known even to the unscientific. There is first the primary coil of copper wire, wound round a hollow reel, with its enclosed bundle of iron wires or solid iron cylinder; then the outer bobbin, or secondary coil of finer copper wire carefully wound around the primary, and insulated at every turn; and finally, as an important adjunct, there is the condensing apparatus, first added by M. Fizeau. In the gigantic instrument recently constructed for Mr. Spottiswoode by Mr. Apps, all these parts are of course represented, but they are of unusual magnitude. The instrument is furnished with two primaries, one or the other being used according to the character of the experiment to be performed. The one used for giving long sparks consists of 660 yards of copper wire, contains 1344 turns, wound singly in six layers, and weighs 55 lbs. ; whilst its core consists of a bundle of iron wire 67 lbs. in weight. The second primary coil, which would be employed for producing short thick sparks, or for spectroscopic purposes, is a helix of 504 yards of similar copper wire, wound in double strand, and weighing 84 lbs. ; its core forms a cylinder of iron wire weighing as much as 92 lbs. It is notable that this primary is ingeniously divided into three separate circuits, which may be used either together or separately. The secondary coil, or that through which the induced current passes, consists of the vast length of 280 miles of fine copper wire, making 341,850 turns, and so carefully insulated that the instrument has been successfully tested with as many as 70 cells of Grove's battery. It need hardly be said that if too great battery power be employed, the insulation may become impaired, and the coil ruined; but the perfection of insulation in the instrument under description is proved by the severe test to which it has been subjected. With 30 quart Grove's cells, a spark 42 inches in length has been obtained. From experiments made with weaker currents, it is estimated that the 42-inch spark would be capable of piercing a solid slab of flint glass six inches in thickness. It may be well supposed that when a current from this powerful coil is transmitted through Giessler vacuum tubes, an illumination of extreme brilliancy and beauty is produced. Experiments already made promise important results in the study of the remarkable stric exhibited in the light of vacuum tubes.

Description of a large Induction Coil,' By William Spottiswoode, F.R.S. Philosophical Magazine, January 1877, p. 30.

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In astronomy the most interesting discovery of late has undoubtedly been that of a new star in the constellation Cygnus. Most readers will remember the famous star of 1866, discovered by Mr. Birmingham, and known as T Coronæ borealis. In that case a very small fixed star suddenly blazed forth and attained to the second magnitude; then slowly faded, with alternations of brightness, during several months, and is now reduced to about the eleventh magnitude. A somewhat similar series of phenomena has been presented to us, ten years later, by the new star in Cygnus. This was first detected on the 24th of last November, at 5h. 41m. P.M., by Dr. Julius Schmidt, the Director of the Observatory at Athens, who is well known as a diligent observer of variable stars. The stranger was situated near p Cygni, and no star in this position had been visible on the last clear night previously, nor is any such star recorded in the Bonn Durchmusterung. When first observed, the star was of the third magnitude, and presented a strong yellow colour. Dr. Schmidt immediately communicated his discovery to Professor Littrow, of Vienna, and to M. le Verrier, of Paris. Unfortunately the state of the sky did not permit of observations at Paris until the 2nd of December, when the Nova was reduced to the fifth magnitude and appeared of a green colour, M. Cornu carefully studied the spectrum by means of a spectroscope applied to the eastern equatorial of the Observatory, and obtained some interesting results. A certain number of bright lines were seen on a faint continuous spectrum, which was almost completely interrupted between the green and the blue, so as to consist apparently of two separate parts. The principal bright lines correspond to those of hydrogen, magnesium, and sodium, or the solar element helium. It need scarcely be remarked that these are some of the chief constituents of the chromosphere or luminous envelope around the sun, whence it might be assumed that the new star possesses an atmosphere similar to that of our central orb. M. Cornu's spectroscopic observations have been confirmed by those of Cazin, Secchi, Vogel, and some other observers. The brilliancy of the star rapidly diminished after its first appearance, so that on the 6th of December it was reduced to the sixth magnitude, and on the 15th of December to the seventh. After this date it ceased to be visible by the naked eye, and continued slowly to wane. It is certainly to be regretted that the discovery was not promptly transmitted to this country, for the appearance of a temporary star is a very rare phenomenon, and we have yet to learn much as to the cause of the rapid variations in brilliancy which such stars present.

Turning from the heavens to the earth, one of the most interesting problems within the range of the physical geographer is that relating

to the origin of inland sheets of salt water. It was formerly supposed that these lakes must have had, at some period of their history, direct communication with the sea-that they were, in fact, large pools of sea-water occupying depressions that had been cut off from communication with the ocean by an elevation of the land. This hypothesis obtained wide credence, and received the assent of such men as Pallas and Humboldt. Of all these inland salt seas, the Dead Sea is unquestionably the most remarkable, on account not less of its excessive degree of saltness than of its great depression below the sea-level. The water is so dense that a gallon of it weighs as much as 124 lbs., and contains in solution nearly 34 lbs. of mineral matter; while, as to the depression, we may remark that the surface of the lake is about 1300 feet below the level of the Mediterranean. The origin of this singular lake was the principal question that the late Duc de Luynes sought to set at rest when, about ten years ago, he started an expedition to Palestine. It was, in fact, the subject above all others to which he directed the attention of Dr. Louis Lartet, whom he attached to the expedition as geologist. After most of the members of the expedition, including the Duke, had returned to France, MM. Lartet and Vignes were left in the East to complete their study of the valley of the Jordan. On M. Lartet's return home he was generously allowed to publish the results of his researches in the shape of communications to the learned societies of Paris, some of which were even reproduced in this country. Quite recently, however, the narrative of the exploration has been published in full by the late Duc's grandson, the Comte de Vogué, and Dr. Lartet has written an accompanying volume on the geological work of the expedition.5

Although we have learnt a good deal about the characters of the Dead Sea and the surrounding country from such writers as De Sauley, Grove, Lynch, Poole, Robinson, Stanley, Van de Velde, and others, yet we have no scientific work on the subject which can be in any way compared for thoroughness with M. Lartet's fine volume. Few writers, indeed, have given the results of strict scientific observation, and even the physical characteristics of the country have been but imperfectly described. Cool scientific investigation shows in fact that the features of the region have been much calumniatedthat instead of the scene of horror and desolation, with evidences of cataclysms at every step and traces of volcanic fire stamped upon. almost every rock, such as some travellers fancy they have seen, we find in reality around the margin of the Dead Sea well-stratified marly beds with siliceous nodules, reminding the writer rather of the strata quietly deposited in the Paris basin than of the chaotic

* Exploration géologique de la Mer-Morte en Palestine et en Idumée. Par Louis Lartet. Paris, 1877.

scenery of a volcanic country. M. Lartet was enabled to make the complete circuit of the lake, and to survey the basin throughout its entire length, thus enjoying opportunities for study which were most unusual, if not unique.

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It appears from the paleontological characters of the most recent marine deposits around the Salt Lake that the country has not been submerged beneath the sea since the Eocene period. But prior to the final emergence of the old sea-bed, even before the Cretaceous strata were deposited, the submarine rocks had been disturbed, and a long line of dislocation established in a north and south direction, which has since been extended by other disturbances. As soon as the new land was exposed to the atmosphere, rain and running water began to work along this old line of fracture, and ultimately hollowed out the valley of the Jordan, and in fact determined the present configuration of the country. Where the depression was greatest the water would naturally accumulate, and a lake, fed by the drainage of the surrounding country, was formed on the site of the Dead Sea as far back as Tertiary times. Having no outlet, the level of the water in the lake would be adjusted by the relation between precipitation and evaporation, being higher or lower according as one or the other predominated. Vast deposits of gypseous marl and other sediments similar to those of the Lisan extend around the margin of the lake, and as they were evidently deposited by its waters they indisputably testify to their former height and extension. It will be seen that according to this view the Dead Sea has always occupied a closed basin, and has from its origin-probably during the Eocene period-been independent of any communication with the ocean. True, the old lacustrine deposits show that the waters once stood more than 100 mètres above their present level; but such au elevation as this would be insufficient to establish communication either with the Mediterranean on the west, from which the lake was always separated by the mountains of Palestine, or with the Red Sea on the south, from which it was cut off by a zone of Cretaceous rocks in the district of the Arabah. Possibly the water of the lake was originally fresh, but has gradually acquired salinity from the brine springs in the neighbourhood, and from the progressive accumulation of salts consequent upon evaporation. Many of the neighbouring marls and limestones are highly saliferous, and have no doubt contributed to the saltness of the Dead Sea; but Dr. Lartet believes that the famous hill of salt, a great deposit at Djebel Usdom, has contributed in only a very subordinate degree. It is notable that the waters are peculiarly rich in bromine, and much of their medicinal virtue is probably due to the presence of salts containing this element. It is known that lepers formerly flocked to the lake, and that the water was actually sent to Rome for the use of wealthy invalids. Dr.

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