402 



SCIENCE. 



[Vol. XIV. No. 358 



perception of an object by the vision of a system of more or less 

 luminous lines forming a kind of pattern. 



The second principle is quite as well known, and is deduced from 

 the duration of the luminous impressions upon the retina, a period 

 of about one-tenth of a second. A series of impressions succeed- 

 ing one another in a very short time produces the effect of simul- 

 taneous impressions ; and it follows, that, in order to perceive the 

 image which we have called the pattern, it is sufficient to receive 

 the luminous impressions of the different lines that constitute it in 

 an interval of time less than one-tenth of a second. 



It was by taking this principle as a basis that Lissajous studied 

 from an optical point of view the vibratory movements of bodies. 

 His experiments are so well known that we need not enter into 

 them here. Lissajous's curves are produced in a rectangular por- 

 tion of a picture. If, on the other hand, this object possesses the 

 power of illumination, all the rays proceeding from the space occu- 

 pied by the curve will, in an exceedingly short space of time, con- 

 verge at one point after having been subjected to a double reflec- 

 tion on the mirrors of the two tuning-forks that were employed for 

 this experiment. 



We may substitute for these forks any movable system whatever, 

 bearing a series of mirrors arranged in such a manner that the 

 displacement of each of them brings upon the same straight line 

 all the rays projected from a portion of an illuminated object. Let 

 us suppose these mirrors to be placed on a circle turning upon an 

 axis perpendicular to its plane, and each of them making a differ- 

 ent angle near 90° with this plane. To each mirror there will be 

 a corresponding series of parallel lines in the picture ; and, if the 

 rotation is sufficiently rapid, all the rays proceeding from the object 

 represented in the picture will meet at the same time, in as short 

 an interval of time as required. It is thus possible to bring to one 

 point all the luminous rays proceeding from a pattern ; and, each 

 portion of the image thus producing its impression upon the' retina 

 in succession, it is sufficient that the interval in which these im- 

 pressions succeed one another should be sufficiently short for them 

 to be rendered simultaneous. 



The transformation of the luminous waves into electric currents 

 is performed by means of a radiophonic receiver forming part of 

 an electric circuit. This receiver may be a cell of selenium, lamp- 

 black, hydrogenated palladium, etc., the resistance of which varies 

 with the quantity of light received. The different portions of the 

 pattern will act differently, according to the quantity of light emanat- 

 ing from them, and in an interval of time less than one-tenth of a 

 second. The variations of resistance of the circuit will correspond 

 to the image observed. 



In order to solve the opposite problem, i.e., to produce this 

 image from the circuit at the receiving station, the writer proposes 

 to employ the gas-telephone, which is an instrument of extreme 

 sensitiveness. It consists of an ordinary telephone in which the 

 portion comprised between the plate, the bobbin, and the inner 

 sides, is in communication with a gas-pipe. The vibrating mem- 

 brane is pierced in the centre with a little hole, through which 

 escapes the gas, which is lighted. This little flame will undergo a 

 variation in brilliancy at each movement of the membrane, and it 

 will produce a continuous succession of rays similar to those con- 

 verging upon the radiophonic receiver. In order to show them, 

 and form an image similar to the pattern, a system of mirrors is 

 employed similar to that used at the first station, but acting in the 

 reverse way. It is evident that these two apparatus must act 

 synchronously, like the Hughes and Baudot regulators employed 

 in telegraphy. Station 2 will reproduce upon a sheet the lines 

 taken upon the image at Station I. 



To sum up, the operation of this theoretical " phoroscope," as it 

 is called, is as follows. The different parts which have been de- 

 scribed being properly combined, the image to be transmitted is 

 broken up into a series of parallel lines, the different points of 

 which act in succession upon a selenium cell, varying the intensity 

 of the current connecting the two stations. These variations in 

 electrical intensity are transformed by the gas-telephone into varia- 

 tions of luminous intensity, and the successive changes of brilliancy 

 of the little flame are projected upon a sheet at points correspond- 

 ing to the various points .of this sheet. Theoretically, nothing can 

 prevent this double transformation of luminous intensity into elec- 



tric intensity, but the realization of the experiment is surrounded 

 with difficulties which make us fear that it will be long before a 

 practical phoroscope is produced ; but this should not discourage 

 enterprising and persevering physicists. 



NOTES AND NEWS. 



Lydia W. Shattuck, for over forty years teacher of botany 

 in Mount Holyoke Seminary, died recently at an advanced age. 



— Professor Daniel Kirkwood, for many years a professor of 

 astronomy in the Indiana State University at Bloomington, has. 

 removed his residence to near Riverside, in southern California. 



— Dr. George M. Sternberg of the army will deliver a lecture 

 before the Brooklyn Institute on Dec. 26. He has selected for his 

 subject " The Methods of Research in Bacteriology," to be illus- 

 trated by living forms of bacterial life thrown upon the screen. 



— C. F. Wheeler of Hubbardston, Mich., has been appointed 

 assistant in the botanical department of the Experiment Station at 

 the Michigan Agricultural College, in place of Eugene Davenport, 

 who has been elected professor of agriculture in the same institu- 

 tion. 



— At the Johns Hopkins University a society of medical students 

 has been organized on the plan of those in Berlin, the object being 

 to bring the men of the various departments into closer connection, 

 to stimulate original research, and to protect the claims of priority 

 of work done by the members. 



— Mr. Austin Corbin's game-forest on Croydon Mountain, Kew 

 Hampshire, has been enriched, says The American Field, by the 

 arrival there last week of a carload of buffaloes, two elks, a moose, 

 deer, and a small band of antelopes. The buffaloes were shipped 

 from Winnipeg, Man., by Buffalo Jones, who herds them there. 



— The great astronomical event of this month will be the total 

 eclipse of the sun, Dec. 22. Various governments have sent out 

 parties to observe the eclipse itself, the United States steamship 

 " Pensacola " having taken a well-equipped party from the United 

 States to St. Paul de Loando, on the west coast of Africa, for this 

 purpose. 



— The greatest depth found by Capt. Spratt in the western 

 Mediterranean basin was between Sicily, Sardinia, and Africa 

 (about 10,600 feet). According to Nature, recent measurements 

 in the eastern basin by Commander Magnaghi of the Italian Navy 

 have yielded, as maximum depth, 13,556 feet, between the Islands 

 of Malta and Candia. 



— A brief outline of the rapid advancement that the practical ap- 

 plication of electricity has made in the last few years is presented 

 in " Everybody's Hand-Book of Electricity," by Edward Trevert, 

 published by Damrell & Upham, Boston. The book is a paper- 

 covered twenty-five cent volume, and treats briefly of electricity 

 and magnetism, dynamos, electric lamps and motors, electric rail- 

 ways, electric welding, measuring instruments, galvanic batteries, 

 and electric bells. It also contains a good glossary of electrical 

 terms, and some useful tables for incandescent wiring. 



— In June of the present year a series of observations on the ve- 

 locity of the wind at the top of the Eiffel Tower was commenced. 

 For this purpose there was erected on the tower, at a height of 995 

 feet above the ground, an autographic anemometer, constructed by 

 Messrs. Richard Brothers of Paris, another of these instruments 

 being at the same time put up at a station situated 1,650 feet 

 from the foot of the tower, the height in this case being about 69 

 feet above the ground. Up to the ist of October last. Engineering 

 states, complete observations had been obtained for loi days ; and 

 from these it appears that, oh an average, the velocity of the wind 

 is about 3.1 times as great at the more lofty station as it is at 

 the lower. Moreover,. the breeze at the top is always fairly strong, 

 as, during the whole of the summer months in which observations 

 were taken, the average velocity of the breeze throughout any given 

 day always exceeded 23 feet per second, and during 21 per cent of 

 the whole period of the observations this average daily velocity was 

 upwards of 33 feet per second. No great storm seems to have oc- 

 curred during the time over which the observations extend, and we 

 do not know the maximum wind-velocity registered during this time. 



