512 Prof. A. G. Bell on the Production of 



W. C. Rontgen *, and W. H. Preece f, I may be permitted 

 to quote from my letter to Mr. Tainter the passage describing 

 the experiments referred to : — 



a Metropolitan Hotel, 



Rue Cainbon, 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 cannot be obtained in the shape 

 of thin diaphragms or in the tubular form ; indeed, the method 

 is specially adapted to testing the generality of the phe- 

 nomenon we have discovered, as it can be adapted to solids, 

 liquids, and gases. 



" Place the substance to be experimented with in a glass 

 test-tube, connnect a rubber tube with the mouth of the test- 

 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 number 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 bichro- 

 mate of potash, crystals of sulphate of copper, and from 

 tobacco-smoke. A whole cigar placed in the test-tube pro- 

 duced a very loud sound. I could not hear any thing from 

 plain water ; but when 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 J, 

 Mr. Tainter communicated to me the results of the experiments 

 he had made in my laboratory during my absence in Europe. 



He had commenced by examining the sonorous properties 

 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 circumstances, he 

 enclosed his materials in a conical cavity in a piece of brass 



* " On the Tones which arise from the intermittent illumination of a 

 gas," see Annalen der Tlxys. und Chemie, Jan. 1881, No. 1, p. 155 : Phil. 

 Mag. April 1881, p. 308. 



t " On the Conversion of Radiant Energy into Sonorous Vibrations/ 

 Proc. Royal Society, March 10, 1881, vol. xxxi. p. 506. 



\ On the 7th of January. 



