ae 
A. G. Bell—Production of Sound by Radiant Energy. 475 
number of sonorous liquids that have so far been found is ex- 
tremely limited, and the sounds produced are so feeble as to 
be heard only by the greatest attention and under the best cir- 
cumstances of experiment. In the experiments made in my 
laboratory a very long test-tube was filled with the liquid under 
examination, and a flexible rubber tube was slipped over the 
mouth far enough down to prevent the possibility of any light 
~ reaching the vapor above the surface. Precautions were also 
taken to prevent reflection from the bottom of the test-tube. 
An intermittent beam of sunlight was then focussed upon the 
liquid in the middle portion of the test-tube by means of a lens 
of large diameter. 
Results. 
Clear water ____- rn eas wee eee No sound audible 
Water discolored. by tak 2.42 2) ee ound. 
WV oo. 2k eee heard. 
Sulphuric ether™.. 25222 :35 32g Feeble, but distinct sound. 
mmoni ae Sita ee aes ee ree sae ag (74 6e ce 66 
Ammonio-sulphate of copper... -- “ ™ = 
Writing nk fe os ee RE Us ee < 
Indigo in sulphurie acid --------- “ gs - “ 
Chloride of copper* - -- -- sos wii . . eg - 
The liquids distinguished by an asterisk gave the best 
sounds, 
Acoustic vibrations are always much enfeebled in passing 
from liquids to gases, and it is probable that a form of experi- 
ment may be devised which will yield better results by com- 
municating the vibrations of the liquid to the ear through the 
medium of a solid rod. 
Experiments with Gaseous Matter. 
On the 29th of November, 1880, I had the pleasure of show- 
ing to Professor Tyndall in the laboratory of the Royal Insti- 
tution the experiments described in the letter to Mr. Tainter, 
from which I have quoted above, and Professor Tyndall at once 
expressed the opinion that the sounds were due to rapid changes 
of temperature in the body submitted to the action of the beam. 
Finding that no experiments had been made at that time to 
test the sonorous properties of different gases, he suggested fill- 
ing one test-tube with the vapor of sulphuric ether (a good ab- 
sorbent of heat), and another with the vapor of bisulphide of 
carbon (a poor absorbent), and he predicted that if any sound 
was heard it would be louder in the former case than in the 
latter. 
The experiment was immediately made, and the result veri- 
fied the prediction. 
