rapid abrupt interruptions of the electric current; while the articulating telephone of Graham Bell was able to transmit speech, since by its essential construction it was able to send undulating currents to the distant receiving station. We may in like manner classify the forms of photophone under two heads, as (1) articulating photophones, and (2) musical photophones; the former being able to transmit speech because they work by beams of light whose intensity can vary in undulatory fluctuations, like those of vocal tones; the latter being able to transmit simple musical tones only, since they work by mere interruptions of a fixed beam of light. Up to the present time, Prof. Bell informs us, the simple receiving disk of ebonite or hard rubber has only served for a musical photophone: the reproduction of the tones of the voice by its means has not yet been demonstrated in practice-at least to his satisfaction. while it produces unmistakable musical tones by the direct action of an intermittent light, in the experiments For made hitherto with articulate speech the instruments have by necessity been so near to one another that the voice of the speaker was audible through the air. Under these circumstances it is extremely difficult to say whether the sounds that are heard proceed from the diaphragm, or whether they merely came through the air to the ear, and if they come from the diaphragm, whether they are really the result of the varying light, and not mere sound vibrations taken up by the disk from the speaker's voice crossing the air. Prof. Bell hopes soon to settle this point, however, by an appeal to experiment on a larger scale with the receiving and transmitting instruments at greater distances apart, and with glass windows in between to shut off all sounds. In Fig. 1 we illustrate the simple musical photophone of Bell and Tainter. It might perhaps be described without injustice as an optical siren, producing sounds from intermittent beams of light, as the siren of Cagniard de Latour produces them from intermittent puffs of air. A beam of light from the sun or from a powerful artificial source, such as an electric lamp, falls upon a mirror M, and is reflected through a large lens L, which concentrates the rays to a focus. Just at the focus is interposed a disk or concave, the degree of its alteration in form varying pierced with holes-forty or so in number-arranged in a with every vibration of the voice. Suppose at any instant circle. This disk can be rotated so that the light is inter-say by a sudden displacement such as takes place when rupted from one to five or six hundred times per second. the letter "T" is sounded-the disk becomes considerably The intermittent beam thus produced is received by a convex; the beam of light will no longer be concentrated lens T, or a pair of lenses upon a common support, whose upon the receiving instrument, but will cover a much function is to render the beam once more parallel, or to wider area. Of the whole beam, therefore, only a relaconcentrate it upon the disk of ebonite placed immediately tively small portion will fall upon the receiving instrubehind, but not quite touching them. From the disk a ment; and it is therefore possible to conceive that, if tube conveys the sounds to the ear. We may remind perfectly adjusted, the illumination should be proporour readers here that this apparent direct conversion of tional to the displacement of the disk, and vary therefore light into sound takes place, as Prof. Bell found, in disks with every vibration with the utmost fidelity. of all kinds of substances hard rubber, zinc, antimony, selenium, ivory, parchment, wood, and that he has lately found that disks of carbon and of thin glass, which he formerly thought exceptions to this property, do also behave in the same way. We may perhaps remark without impropriety that it is extremely improbable that the apparent conversion of light into sound is by any means a direct process. It is well known that luminiferous rays, when absorbed at the surface of a medium, warm that surface slightly, and must therefore produce physical and molecular actions in its structure. If it can be shown that this warming effect and an intermediate cooling by conduction can go on with such excessive rapidity that beams of light falling on the surface at intervals less than the hundredth of a second apart produce a discontinuous molecular action of alternate expansion and contraction, then the mysterious property of matter revealed by these experiments is accounted for. However this may be, the musical photophone, as represented in Fig. 1, produces very distinct sounds, of whose existence and dependence for their production on the light the listener may satisfy himself by cutting off the light at any moment with the little opaque disk fixed on the end of the little lever just in front of the holes in disk R, and which can be worked by a Morse key like a telegraph instrument, thus producing at will alternate sounds and silences. With this musical photophone sounds have been carried by an interrupted beam of light for a distance exceeding a mile; there appears, indeed, | The receiver of the articulating photophone is shown on the right-hand side of the diagram (Fig. 2) sketched by Prof. Bell. A mirror of parabolic curve C C serves to concentrate the beam and to reflect it down upon the selenium cell s, which is included in the circuit of a battery P along with a pair of telephones T and T. Here again a general view like that given in Fig. 6 facilitates the comprehension of the principal parts of the apparatus. The sensitive selenium cell is seen in the hollow of the parabolic mirror which is mounted so as to be turned in any desired direction. The battery standing upon the ground furnishes a current which flows through the selenium cell and through the telephones. When a ray of light falls on the selenium-be it for ever so short an instant-the selenium increases in conductivity, and instantly transmits a larger amount of electricity, and the observer with the telephones hears the ray, or the succession of them ;-hears M N FIG. 4.-Diagram to show the action of the Selenium Receiver. The articulating photophone is that to which hitherto indeed their every fluctuation in a series of sounds which, public attention has been most largely directed, and in since each vibration corresponds to a vibration of the voice which a selenium receiver plays a part. Fig. 2 gives in of the distant speaker, reproduce the speaker's tones. diagram form the essential parts of this arrangement. A The great difficulty to be overcome in the use of mirror M reflects a beam of light as before through a lens selenium as a working substance arose from its very L, and (if desired for the purpose of experimentally cutting high resistance. To reduce this to the smallest possible off the heat-rays) through a cell A containing alum-water, quantity, and at the same time to use a sufficiently large and casts it upon the transmitter B. This transmitter, surface whereon to receive the beam of light, was the shown again in Fig. 5, consists of a little disk of thin problem to be solved before any practical result could be glass, silvered on the front, of about the size of the disk arrived at. After many preliminary trials with gratings of an ordinary telephone, and mounted in a frame, with and perforated disks of various kinds, Prof. Bell and Mr. a flexible india-rubber tube about sixteen inches long Tainter finally settled upon the ingenious device to be leading to a mouthpiece. A second lens R, interposed in described. A number of round brass disks, about two the beam of light after reflection at the little mirror, inches in diameter, and a number of mica disks of a renders the rays approximately parallel. The general view diameter slightly less, were piled upon one another so as of the transmitting apparatus given in Fig. 5 enables the to form a cylinder about two and a half inches in length. relative sizes and positions of the various parts (minus They were clamped together from end to end, the clampthe alum-cell which is omitted) to be seen. The screwing rods also serving to unite the disks of brass electrically adjustments of the support serve to direct the beam of light in the desired direction. It may be well to explain once for all how the vibrations of the voice can affect the intensity of the reflected beam far away. The lenses are so adjusted that when the mirror B is flat (ie. when not vibrating) the beam projected from the apparatus to the distant station shall be nearly focussed on the receiving instrument. Owing to the optical difficulties of the problem it is impossible that the focussing can be more than approximate. Now, matters being thus arranged, when the speaker's voice is thrown against the disk B it is set into vibration, becomes alternately bulged out and in, and made slightly convex in two sets, alternate disks being joined, the 1st, 3rd, 5th, &c., being united together, and the 2nd, 4th, 6th, &c., being united in another series. This done, the edges between the brass disks were next filled with seleninum, which was rubbed in at a temperature sufficiently high to reach the melting-point of selenium. After this the selenium was carefully annealed to bring it into the sensitive crystalline state. Then the cell is placed in a lathe and the superfluous selenium is turned off until the edges of the brass disks are bared. Fig. 3 shows, in section, the construction of such a cell. Prof. Bell has also used cells in which the selenium filled only the alternate spaces between disks, the intermediate spaces being occupied by mica disks of equal diameter with the brass disks. But this arrangement was in no way preferable, for in practice connecting the alternate disks; and secondly, that the current from the battery P cannot go round the telephone circuit without passing somewhere through selenium from one brass disk to the next. The special advantages of the "cell" devised by Prof. Bell are that in the first place the thickness of the selenium that the current must traverse is nowhere very great; that in the second, this photo-electrical action of light on selenium being almost entirely a surface action, the arrangement by which all the selenium used is a thin surface film could hardly be improved upon; and that thirdly, the symmetry of the cylindrical cell specially adapts it for use in the parabolic mirror. These details will be of great interest especially to those who desire to repeat for themselves the experimental transmission of sound by light. The greatest distance to which articulate speech has yet been transmitted by the selenium-cell-photophone is 213 metres, or 233 yards. When sunlight is not available recourse must be had to an artificial source of sufficient power. During the recent experiments made by Prof. Bell in Paris the weather has been adverse, and the electric light has been called into requisition in the ateliers of M. Bregnet (Fig. 7, which is kindly supplied us by Prof. Bell). The distance in these experiments between the transmitting diaphragm B and the parabolic reflector C C of the receiver was fifteen metres, the entire length of the room in which FIG. 7.-The Photophone with Electric Light. the experiments were made. Since at this distance the spoken words were themselves perfectly audible across the air, the telephones connected with the selenium-cell were placed in another apartment, where the voices were heard without difficulty and without doubt as to the means of transmission. Of the earlier and less perfect forms of the photophone little need be said. One device, which in Prof. Bell's hands worked very successfully over a distance of eightysix yards, consisted in letting the beam of light pass through a double grating of parallel slits lying close to one another, one of which was fixed, the other movable and attached to a vibrating diaphragm. When these were placed exactly one in front of the other the light could traverse the apparatus, but as the movable grating slid more or less in front of the fixed one more or less of the light was cut off. Speaking to the diaphragm therefore caused vibrations which shut or opened, as it were, a door for the beam of light, and altered its intensity. The mirror transmitter of thin glass silvered was however found superior to all others; and it is hard to see how it could be improved upon, unless possibly by the use of a thin disk of silver itself accurately surfaced and polished. Whatever be the future before the photophone, it assuredly deserves to rank in estimation beside the now familiar names of the telephone and the phonograph. NOTES THE Triennial Gold Medal of the Chemical Section of the Philosophical Society of Glasgow, founded in commemoration of the work of Thomas Graham, F.R.S., late Master of the Mint, will be awarded, at the end of the present session, for the best paper on any subject in pure or applied chemistry. Authors are requested to send in their papers not later than February 1, 1881, addressed to the Secretary of the Section, Dr. J. J. Dobbie, Chemical Laboratory, University of Glasgow. THE annual meeting of the five academies which constitute the French Institute was held on Monday last week, when M. E. Levasseur gave an address on the Ethnography of France, and Col. Perrier described the operation he undertook to connect geodetically Algeria and Spain. THE Royal Institution Lecture arrangements (not yet complete) for the ensuing season (before Easter) will include the Christmas course by Prof. Dewar; and courses by Professors Tyndall and Schäfer, the Rev. William Haughton, the Rev. H. R. Haweis, Mr. H. H. Statham, Mr. Reginald S. Poole, and others. Friday Evening Discourses will probably be given by Mr. Warren De La Rue, Prof. Tyndall, Sir John Lubbock, Sir William Thomson, Dr. J. Burdon Sanderson, Dr. Andrew Wilson, Dr. Arthur Schuster, Mr. Alexander Buchan, Dr. W. H. Stone, Dr. W. J. Russell. THE death is announced of Sir Thomas Bouch, the engineer of the Tay Bridge. It is believed that his system received a severe shock on account of the Tay Bridge disaster and the proceedings consequent on it. M. ERHARD, the well-known French cartographer, died on October 23. M. Erhard was a naturalised Frenchman, having been born at Freiburg im Breisgau. AMONG Mr. Stanford's announcements of forthcoming works are the following:-" Prehistoric Europe: a Geological Sketch," by Dr. James Geikie, F.R.S.; a fourth edition of "The CoalFields of Great Britain," by Prof. Edward Hull, F.R.S.; "Life and her Children: Glimpses of Animal Life from the Amoeba to the Insects," by Arabella B. Buckley; "Index Geographicus Indicus: a Gazetteer of India," by J. F. Barness; "The Flora of Algeria, considered in Relation to the Physical History of the Mediterranean Region and Supposed Submergence of the Sahara," by W. Mathews; "Water Supply of England and Wales: its Geology, Underground Circulation, Surface Distribution, and Statistics," by C. E. de Rance. IN the November number of Scribner's Monthly is a curious article on Second Sight or Clairvoyance, by an "Ex-Conjuror " (Mr. Henry Hatton), in which it is shown that the whole thing is an elaborate system of mnemonics. The article has all the appearance of being genuine. IN reference to the notice in NATURE, vol. xxii. p. 587, on the address of Dr. Karl Zittel on the subject of the geology of the Libyan Desert, we should state that while the paper contains Zittel's opinions of the observations and collections of other travellers, it is mainly derived from the Professor's personal examination of the physiography of that country, and of the fossils which he there collected, when, as a member of the expedition under the leadership of Dr. Rohlfs, he visited the Libyan Desert in the winter of 1873-74. THE lecture on "The Modifications of the External Aspects of Organic Nature produced by Man's Interference," delivered by Prof. Rolleston to the Royal Geographical Society in 1879, has just been published in that Society's Journal. Amongst other interesting matters Prof. Rolleston rectifies an error into which all or most translators of Cæsar [have fallen respecting the Scotch fir. Cæsar ("De Bello Gallico," v. 12) says of Britain, "Materia cujusque generis, ut in Gallia, est præter fagum atque abietem," which words have been generally taken to mean, "There is wood of all kinds to be found in Britain, as in Gaul, except the beech and the fir." The word præter however does not always mean "except," but sometimes "besides," as quotations from Cicero and Plautus aptly illustrate. Prof. Rolleston further remarks that "an historian who was or was not a professed botanist, might without any sensible man blaming him, speak nowadays of all the common pines 'Scotch,' 'umbrella,' 'cluster,' &c., as 'pines'; my present belief is that Julius would similarly have spoken of them all as abietes, and would probably have included the 'firs' proper under the same name as these 'pines.'' AT the last meeting of the Epping Forest and County of Essex Naturalists' Field Club, held Saturday, October 30, it was announced that H.R. H. the Duke of Connaught, Ranger, had consented to become the Patron of the Club. Arrangements are being made to get up a course of winter science lectures in connection with the Club, the first of these being fixed for November 10, by Mr. J. E. Harting, who will lecture on "Forest Animals." It was further announced that a lecture had been promised during the session by Mr. A. R. Wallace. PROF. BOYD DAWKINS has lately shown in his "Early Man in Britain" that "although the Neolithic men were imineasurably above the Cave men in culture, they were far below them in the arts of design;" and further that the Cave-man " possessed a singular talent for representing the animals he hunted, and his sketches reveal to us that he had a capacity for seeing the beauty and grace of natural form not much inferior to that which is the result of long-continued civilisation in ourselves, and very much higher than that of his successors in Europe in the Neolithic age.' That this faculty of design or artistic aptitude is still independent of advanced or advancing civilisation is shown by Dr. Holub in a paper "On the Central South African Tribes," just published in the Journal of the Anthropological Institute. Mr. Holub remarks in connection with the Bushmen, that these people "regarded as the lowest types of Africans, in one thing excel all the other South African tribes whose acquaint ance I made between the south coast and 10° south latitude. I have in my possession about 200 sketches on wood and stone and ostrich shells, by various tribes, but every one who knows anything about drawing must acknowledge that those which were done by Bushmen are superior to any of the others." IT is stated that some samples of a new seed and also of the native cucumber, collected in Central Australia by Mr. Vesey Brown, have been received at the Sydney Botanical Gardens. The former is a small black pea, which grows in pods similar to those of the ordinary pea; it is supposed to be edible, and resembles the nardoo. The cucumbers are about the size of walnuts, and are said to make an excellent pickle. A RECENT report to the Foreign Office by Mr. Consul Crawford at Oporto on matters connected with the wine trade contains observations on the ravages of the parasitic insect, Phylloxera vastatrix, in the port wine district, and the means taken to avert them, and is illustrated by a sketch map of Northern Portugal, showing the progress of the disease. Ar the opening meeting of the Eastbourne Natural History Society on October 15, Mr. F. C. S. Roper read a paper on the additions to the fauna and flora of the Cuckmere district during the past year. IN the Fourteenth Annual Report of the Aëronautical Society of Great Britain are papers on Aeronautics, by Mr. T. Moy, the "Mechanical Action of the Air," by Mr. Phillips; "Artificial Flight," by Mr. F. W. Brearey; "Aërial Propellers," by Mr. | R. C. Jay. VALPARAISO advices to August 21 give particulars of the earthquake of August 14. The Chilian Times says:-"The duration of the shock was nearly ninety seconds. No serious damage was done to buildings in Valparaiso. At Vina del Mar, one of the towers of the church fell and another was shaken out of its level, and will probably have to be pulled down. The roof of the Quillota parish church fell in. At Llaillai eighteen or twenty houses were destroyed. Illapel suffered very severely. One strange item reported is the occurrence of 'huracane de agua,' whatever they may be. The Governor of Illapel in his first telegram stated that three of these had burst in the Cordillera. Now it is stated that there were thirty observed. One paper spoke of them as 'water volcanoes.' From Coquimbo it is reported that high columns of water were thrown up from the bay. An employé of the Transandine Telegraph Company felt the shock while crossing the highest parts of the Andes. He states that it was the strongest earthquake he has ever felt." A NAPLES telegram of November 2 states that Vesuvius is now very active; lava continues to flow from the crater, and present indications point to the probability of increased eruptive energy. De THE first meeting of the Society of Arts is announced for November 17, when the opening address will be delivered by F. J. Bramwell, F.R.S., Chairman of the Council. Before Christmas the following papers will be read :-November 24"Barry's Influence on English Art," by J. Comyns Carr. cember I-"The Photophone," by W. H. Preece. December S -"London Fogs," by Dr, A. Carpenter. December 15"The Use of Sound for Signals," by E. Price Edwards. The following papers are down on the list for reading after Christmas:- -"Buying and Selling: its Nature and its Tools," by Prof. Bonamy Price. "The Participation of Labour in the Profits of Enterprise," by Sedley Taylor, M.A., late Fellow of Trinity College, Cambridge. "The Gold Fields of India," by Hyde Clarke. "Flashing Signals for Lighthouses," by Sir William Thomson, F.R.S. "The Present Condition of the Art of Wood-carving ia England," by J. Hungerford Pollen, "Ten Years' Experience of the Working of the Trade Mark Act," by E. C. Johnson. "Trade Prospects," by Stephen Bourne. "The Manufacture of Aerated Waters," by T. B. Bruce Warren. "The Compound Air Engine," by Col. F. Beaumont, R.E. "Improvements in the Treatment of Esparto for the Manufacture of Paper," by William Arnot, F. C.S. "Deep Sea Investigation, and the Apparatus used in it," by J. Y. Buchanan. "The Discrimination and Artistic Use of Precious Stones," by Prof. A. H. Church. "Indian Agriculture," by W. R. Robertson. Five courses of lectures are announced under the Cantor bequest: First course-] e-Five lectures on "Some Points of Contact between the Scientific and Artistic Aspects of Pottery and Porcelain," by Prof. A. C. Church. Second Course-Three lectures on "Watchmaking," by Edward Rigg, M.A. Third course-Four lectures on "The Scientific Principles involved in Electric Lighting," by Prof. W. G Adams, F.R.S. Fourth course-Three lectures on "The Art of Lace-making," by Alan S. Cole. Fifth course-Three lec"Colour Blindness and its Influence upon Various Industries," by R. Brudenell Carter. The two Juvenile Lectures, for children of Members, during the Christmas holidays, will be by G. J. Romanes, F.R.S., on "Animal Intelligence." The arrangements for the "Indian," "Foreign and Colonial," and "Chemical and Physical" Sections will be announced after Christmas. tures on THE following is the title of the essay to which the "Howard Medal" of the Statistical Society will be awarded in November, |