252 



SCIENCE. 



(4.) If the tuning-fork (A) in Fig. II is thrown into 

 vibration by an undulatory instead of an intermittent 

 current passed through the electro-magnet (B), it is prob- 

 able that a musical tone, electrically produced 'in the 

 receiver (F) by the action of the same current, would 

 be found capable of extinguishing the effect produced in 

 the receiver (G) by the action of the undulatory beam of 

 light, in which case it should be possible to establish an 

 acoustic balance between the effects produced by light 

 and electricity by introducing sufficient resistance into 

 the electric circuit. 



UPON THE NATURE OF THE RAYS THAT PRODUCE 

 SONOROUS EFFECTS IN DIFFERENT SUBSTANCES. 

 In my paper read before the American Association last 

 August and in the present paper I have used the word 

 "light "in its usual rather than its scientific sense, and 1 

 have not hitherto attempted to discriminate the effects 

 produced by the different constituents of ordinary light, 

 the thermal, luminous, and actinic rays. I find, however, 

 that the adoption of the word " photophone " by Mr. 

 Tainter and myself has led to the assumption that we 

 believed the audible effects discovered by us to be due 

 entirely to the action of luminous rays. The meaning 

 we have uniformly attached to the words " photophone " 

 and " light " will be obvious from the following passage, 

 quoted by my Boston paper : 



" Although effects are produced as above shown by 

 forms of radiant energy, which are invisible, we have 

 named the apparatus for the production and reproduc- 

 tion of sound in this way the '.photophone ' because an 

 ordinary beam of light contains the rays which are 

 operative." 



To avoid in future any misunderstandings upon this 

 point we have decided to adopt the term "radiophone," 

 proposed by M. Mercadier, as a general term signifying 

 an apparatus for the production of sound by any form 

 of radiant energy, limiting the words thermophone, pho- 

 tophone, and actinophone, to apparatus for the production 

 of sound by thermal, luminous, or actinic rays respec- 

 tively. 



M. Mercadier, in the course of his researches in radio- 

 phony, passed an intermittent beam from an electric lamp 

 through a prism, and then examined the audible effects 

 produced in different parts of the spectrum. {Comptes 

 Rendus, Dec. 6th, 1880.) 



We have repeated this experiment, using the sun as our 

 source of radiation, and have obtained results somewhat 

 different from those noted by M. Mercadier. 



A beam of sunlight was reflected from a heliostat 

 (A, Fig. I2*j through an achromatic lens, (B) so as to 

 form an image of the sun upon the slit (C). 



The beam then passed through another achromatic 

 lens (D) and through a bisulphide of carbon prism (E), 

 forming a spectrum of great intensity, which, when 

 focussed upon a screen, was found to be sufficiently 

 pure to show the principal absorption lines of the solar 

 spectrum. 



The disk-interrupter (F) was then turned with sufficient 

 rapidity to produce from five to six hundred interruptions 

 of the light per second, and the spectrum was explored 

 with the receiver (G), which was so arranged that the 

 lamp-black surface exposed was limited by a slit, as 

 shown. 



Under these circumstances sounds were obtained in 

 every part of the visible spectrum, excepting the extreme 

 half of the violet, as well as in the ultra-red. A continu- 

 ous increase in the loudness of the sound was observed 

 upon moving the receiver (G) gradually from the violet into 

 the ultra-red. The point of maximum sound lay very far 

 out in the ultra-red. Beyond this point the sound began 

 to decrease, and then stopped so suddenly that a very 

 slight motion of the receiver (G) made all the difference 

 between almost maximum sound and complete silence. 



♦See page 249 for illustrations. 



(2.) The lamp-blacked wire gauze was then removed and 

 the interior of the receiver (G) was filled with red-worsted. 

 Upon exploring the spectrum as before, entirely different 

 results were obtained. The maximum effect was pro- 

 duced in the green at that part where the red worsted ap- 

 peared to be black. On either side of this point the 

 sound gradually died away, becoming inaudible on the 

 one side in the middle of the indigo, and on the other at a 

 short distance outside the edge of the red. 



(3.) Upon substituting green silk for red worsted the 

 limits of audition appeared to be the middle of the blue 

 and a point a short distance out in the ultra-red. Maxi- 

 mum in the red. 



(4.) Some hard-rubber shavings were now placed in 

 the receiver (G). The limits of audibility appeared to be on 

 the one hand the junction of the green and blue, and on 

 the other the outside edge of the red. Maximum in the 

 yellow. Mr. Tainter thought he could hear a little way 

 into the ultra-red, and to his ear the maximum was 

 about the junction of the red and orange. 



(5.) A test-tube containing the vapor of sulphuric ether 

 was then substituted for the receiver (G). Commencing at 

 the violet end, the test-tube was gradually moved down 

 the spectrum and out into the ultra-red without audible 

 effect, but when a certain point far out in the ultra-red 

 was reached a distinct musical tone suddenly made its 

 appearance, which disappeared as suddenly on moving 

 the test-tube a very little further on. 



(6.) Upon exploring the spectrum with a test-tube con- 

 taining the vapor of iodine the limits of audibility ap- 

 peared to be the middle of the reel and the junction of 

 the blue and indigo. Maximum in the green. 



(7.) A test-tube containing peroxide of nitrogen was 

 substituted for that containing iodine. Distinct sounds 

 were obtained in all parts of the visible spectrum, but no 

 sounds were observed in the ultra-red. 



The maximum effect seemed to me to be in the blue. The 

 sounds were well marked in all parts of the violet, and I 

 even fancied that the audible effect extended a little way 

 into the ukra-violet, but of this I cannot be certain. Upon 

 examining the absorption spectrum of peroxide of nitro- 

 gen it was at once observed that the maximum sound 

 was produced in that part of the spectrum where the 

 greatest number of absorption lines made their appear- 

 ance. 



(8.) The spectrum was now explored by a. selenium 

 cell, and the audible effects were observed by means of 

 a telephone in the same galvanic circuit with the cell. 

 The maximum effect was produced in the red. The aud- 

 ible effect extended a little way into the ultra-red on the 

 one hand and up as high as the middle of the violet on 

 the other. 



Although the experiments so far made can only be 

 considered as preliminary to others of a more refined na- 

 ture, I think we are warranted in concluding that the 

 nature of the rays that produce sonorous effects in dif- 

 ferent substances depends upon the nature of the sub- 

 stances that are exposed to the beam, and that the sounds 

 are in every case due to those rays of the spectrum that 

 are absorbed by the body. 



The Spectrophone. 



Our experiments upon the range of audibility of differ- 

 ent substances in the spectrum have led us to the con- 

 struction of a new instrument for use in spectrum analy- 

 sis, which was described and exhibited to the Philosophi- 

 cal Society of Washington last Saturday.* The eye-piece 

 of a spectroscope is removed, and sensitive substances 

 are placed in the focal point of the instrument behind an 

 opaque diaphragm containing a slit. These substances 

 are put in communication with the ear by means of a 

 hearing tube, and thus the instrument is converted into a 

 veritable "spectrophone " like that shown in Fig. 1 3-t 



* Proc. ol Phil. Soc. of Washington, April 16, 1881. 

 fSee page 250 for illustrations. 



