152 BULLETIN OF THE 



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 No sound audible. 



Water discolored by ink Feeble sound. 



Mercury No sound heard. 



Sulphuric ether* • Feeble, but distinct sound. 



Ammonia " " 



Ammonia-sulphate of copper " " 



Writing ink " " 



Indigo in sulphuric acid " " 



Chloride of copper* " " 



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 experiment may 

 be devised which will yield better results by communicating 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, 1 had the pleasure of showing 

 to Prof. Tyndall, iu the laboratory of the Royal Institution, the 

 experiments described in the letter to Mr. Taiuter from which I 

 have quoted above, and Prof. 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 ex- 

 periments had been made at that time to test the sonorous properties 

 of different gases, he suggested filling one test-tube with the vapor 

 of sulphuric ether, (a good absorbent of heat,) and another with 

 the vapor of bi-sulphide of carbon, (a poor absorbent,) aud 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 verified 

 the prediction. 



