i88 



THE POPULAR SCIENCE MONTHLY. 



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, althougli 

 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 Wash- 

 ington. 1 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- 

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



Upon my return to Washington in the early part of January,* Mr. 

 Tainter communicated to me the results of the experiments he had 

 made in my laboratory during my absence in Europe. 



lie had commenced by examining the sonorous properties of a vast 

 number of substances inclosed in test-tubes in a simple empirical search 

 for loud effects. He was thus led gradually to the discovery that cot- 

 ton-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 inclosed 

 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 con- 

 nection with the hearing-tube. When this conical cavity was stuffed 

 with worsted or other fibrous materials the sounds produced were much 

 louder than when a test-tube was employed. This form of receiver is 

 shown in Fig. 1. 



Fig. 1. 



Mr. Tainter next collected silks and worsteds of different 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 comparison. Not having any at hand, however, 

 he tried the effect of darkening some cotton-wool with lampblack. 



* On the '7th of January. 



