A. G. Bell—Production of Sound by Radiant Energy. 465 
feeble sound was heard. I would suggest that you might repeat 
these experiments and extend the results,” &c., d&e. 
Experiments with Solids. 
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. 
He had commenced by examining the sonorous properties of 
a vast number of substances enclosed in test-tubes in a simple 
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 
closed by a flat plate of glass. A brass tube leading into the 
cavity served for connection with the hearing-tube. hen 
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 
figure 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 lamp-black. Such a marked reinforcement of the 
sound resulted that he was induced to try lamp-black alone. 
* On the 7th of January. 
