PHILOSOPHICAL SOCIETY OF WASHINGTON. 153 



Since the publication of the memoirs of Rontgen* and Tyndallf 

 we have repeated these experiments, and have extended the inquiry 

 to a number of other gaseous bodies, obtaining in every case sim- 

 ilar results to those noted in the memoirs referred to. 



The vapors of the following substances were found to be highly 

 sonorous in the intermittent beam : Water vapor, coal gas, sulphuric 

 ether, alchohol, ammonia, amylene, ethyl bromide, diethylamene, 

 mercury, iodine, and peroxide of nitrogen. The loudest sounds 

 were obtained from iodine and peroxide of nitrogen. 



I have now shown that sounds are produced by the direct action 

 of intermittent sunlight from substances in every physical condition, 

 (solids, liquid, and gaseous,) and the probability is therefore very 

 greatly increased that sonorousness under such circumstances will be 

 found to be a universal property of matter. 



Upon Substitutes for Selenium in Electrical Receivers. 



At the time of my communication to the American Association 

 the loudest effects obtained were produced by the use of selenium, 

 arranged in a cell of suitable construction, and placed in a galvanic 

 circuit with a telephone. Upon allowing an intermittent beam of 

 sunlight to fall upon the selenium a musical tone of great intensity 

 was produced from the telephone connected with it. 



But the selenium was very inconstant in its action. It was rare- 

 ly, if ever, found to be the case, that two pieces of selenium (even 

 of the same stick) yielded the same results under identical circum- 

 stances of annealing, &c. While in Europe last autumn, Dr. Chi- 

 chester Bell, of University College, London, suggested to me that 

 this inconstancy of result might be due to chemical impurities in 

 the selenium used. Dr. Bell has since visited my laboratory in 

 Washington, and has made a chemical examination of the various 

 samples of selenium I had collected from different parts of the 

 world. As I understand it to be his intention to publish the results 

 of this analysis very soon, I shall make no further mention of his 

 investigation than to state that he has found sulphur, iron, lead, and 

 arsenic in the so-called " selenium," with traces of organic matter ; 

 that a quantitative examination has revealed the fact that sulphur 

 constitutes nearly one per cent, of the whole mass ; and that when 



* Ann. der Phys. und Chem., 1881, No. 1, p. 155. 

 •j- Proc. Roy. Soc, vol. xxxi, p. 307. 



