SCIENCE. 



243 



and in Europe by M. Mercadier.t Prof. Tyndall.J W. E. 

 R6ntgen,§ and W. H. PreeceJ I may be permitted to 

 quote from my letter to Mr. Tainter the passage describ- 

 ing the experiments referred to : 



Metropolitan Hotel, Rue Cambon, Paris, 



Nov. 2, 1880. 



Dear Mr. Tainter: 



* * * I have devised a method of producing sounds by the 

 action of an intermittent beam of light from substances that can- 

 not be obtained in the shape of thin diaphragms or in the tubular 

 form; indeed, the method is specia'lv adapted to testing the gen- 

 erality of the phenomenon we have discovered, as it can be adapt- 

 ed to solids, liquids, and gases. 



Place the substance to be experimented with in a glass test-tube, 

 connect a rubber tube with the mouth of the tebt-tube, placing the 

 other end of the pipe to the ear. Then focus the intermittent 

 beam upon the substance in the tube. I have tried a large num- 

 ber of substances in this way with great success, although it is 

 extremely difficult to get a glimpse Of the sun here, and when it 

 does shine the intensity of the light is not to be compared with 

 that to be obtained in Washington. I got splendid effects from 

 crystals of bichromate of potash, crystals of sulphate of copper, 

 and from tobacco smoke. A whole cigar placed in the test-lube 

 produced a very loud sound. I could not hear anything from 

 plain water, but whei the water was discolored with ink a feeble 

 sound was heard. I would suggest that you might repeat these 

 experiments and extend the results," &c, &c. 



Upon my return to Washington in the early part of 

 January.tt Mr. Tainter communicated to me the experi- 

 ments he had made in my laboratory during my absence 

 in Europe. 



He had commenced by examining the sonorous proper- 

 ties of a vast number of substances enclosed in test-tubes 

 in a simple empirical search for loud effects. He was 

 thus led gradually to the discovery that cotton-wool, 

 worsted, silk, and fibrous materials generally, produced 

 much louder sounds than hard rigid bodies like crystals, 

 or diaphragms such as we had hitherto used. 



In order to study the effects under better circum- 

 stances he enclosed his materials in a conical cavity in a 

 piece of brass closed by a flat plate of glass. A brass 

 tube leading into the cavity served for connection with 

 the hearing-tube. When this conical cavity was stuffed 

 with worsted or other fibrous materials the sounds pro- 

 duced were much louder than when a test-tube was em- 

 ployed.- This form of receiver is shown in Fig. 1. 



Mr. Tainter next collected silks and worsteds of differ- 

 ent colors, and speedily found that the darkest shades 

 produced the best effects. Black worsted especially gave 

 an extremely loud sound. 



As white cotton-wool had proved itself equal, if not 

 superior, to any other white fibrous material before tried, 

 he was anxious to obtain colored specimens for compari- 

 son. ' Not having any at hand, however, he tried the 

 effect of darkening some coCton-wool with lamp-black. 

 Such a marked re-enforcement of the sound resulted that 

 he was induced to try lamp-black alone. 



About a teaspoonful of lamp-black was placed in a 

 test-tube and exposed to an intermittent beam of sun- 

 light. The sound produced was much louder than any 

 heard before. N 



Upon smoking a piece of plate-glass, and holding it in 

 the intermittent beam with the lamp-black surface to- 

 wards the sun, the sound produced was loud enough to 

 be heard, with attention, in any part of the room. With 

 the lamp black surface turned from the sun the sound 

 was much feebler. 



Mr. Tainter repeated these experiments for me im- 

 mediately upon my return to Washington, so that I 

 might verify his results. 



t " Notes on Radiophony," Comfits Rendu*, Dec, 6 and 13, 1880 ; Feb. 

 21 and 28, 1881. See, also, Journal de Physique, vol. x, p. 53. 



t" Action of an Intermittent Beam of Radiant Heat upon Gaseous 

 Matter." Proc. Royal Society, Jan. 13, 1881, vol. xxxi, p. 307. 



§ " On the tones which arise from the intermittent illumination of a 

 gas." See Anna/en der Phys. und Chemie, Jan., 1881, No. 1, p. 155. 



ll"On the Conversion of Radiant Energy into Sonorous Vibrations." 

 Proc. Royal Society, March 10, r83i, vol. xxxi, p. 506. 



ttOn the 7th of January. 



Upon smoking the interior of the conical cavity shown 

 in Fig. 1, and then exposing it to the intermittent beam, 

 with the glass lid in position as shown, the effect was 

 perfectly startling. The sound was so loud as to be 

 actually painful to an ear placed closely against the end 

 of the hearing-tube. 



The sounds, however, were sensibly louder when we 

 placed some smoked wire gauze in the receiver, as 

 illustrated in the drawing, Fig. I.* 



When the beam was thrown into a resonator, the in- 

 terior of which had been smoked over a lamp, most 

 curious alternations of sound and silence were observed. 

 The interrupting disk was set rotating at a high rate of 

 speed, and was then allowed to come gradually to rest. 

 An extremely feeble musical tone was at first heard, 

 which gradually fell in pitch as the rate of interruption 

 grew less. The loudness of the sound produced varied 

 in the most interesting manner. Minor re-inforcements 

 were constantly occurring, which became more and more 

 marked as the true pitch of the resonator was neared. 

 When at last the frequency of interruption corresponded 

 to the frequency of the fundamental ot the resonator, the 

 sound produced was so loud that it might have been 

 heard by an audience of hundreds of people. 



The effects produced by lamp-black seemed to me to 

 be very extraordinary, especially as I had a distinct 

 recollection of experiments made in the Summer of 1880 

 with smoked diaphragms, in which no such re-enforce- 

 ment was noticed. 



Upon examining the records of our past photophonic 

 experiments we found in vol. vii, p. 57, the following 

 note : 



" Experiment V. — Mica diaphragm covered with lamp- 

 black on side exposed to light. 



" Result: distinct sound about same as without lamp- 

 black. — A, G. B. July lSl/i, 1880. 



" Verified the above, but think it somewhat louder 

 than when used without lamp-black. — S. T., July 18//1, 

 1880. 



Upon repeating this old experiment we arrived at the 

 same result as that noted. Little if any augmentation 

 of sound resulted from smoking the mica. In this ex- 

 periment the effect was observed by placing the mica 

 diaphragm against the ear and also by listening through 

 a hearing-tube, one end of which was closed by the 

 diaphragm. The sound was found to be more audible 

 through the free air when the ear was placed as near to 

 the lamp-black surface as it could be brought without 

 shading it. 



At the time of my communication to the American 

 Association I had been unable to satisfy myself that the 

 substances which had become sonorous under the direct 

 influence of intermittent sunlight were capable of repro- 

 ducing the sounds of articulate speech under the action 

 of an undulatory beam from our photophonic transmitter. 

 The difficulty in ascertaining this will be understood by 

 considering that the sounds emitted by thin diaphragms 

 and tubes were so feeble that it was impracticable to pro- 

 duce audible effects from substances in these conditions 

 at any considerable distance away from the transmitter ; 

 but it was equally impossible to judge of the effects pro- 

 duced by our articulate transmitter at a ?hort distance 

 away because the speaker's voice was directly audible 

 through the air. The extremely loud sounds produced 

 from lamp-black have enabled us to demonstrate the 

 feasibility of using this substance in an articulating photo- 

 phone in place of the electrical receiver formerly employed. 



The drawing (Fig. 2*) illustrates the mode in which the 

 experiment was conducted. The diaphragm of the trans- 

 mitter (A) was only 5 centimetres in diameter, the diameter 

 of the receiver (B ) was also 5 centimetres, and the distance 

 between the two was 40 metres, or 800 times the 

 diameter of the transmitting diaphragm. We were 

 unable to experiment at greater distances without 



*See page 247 for illustrations. 



