36 THE POPULAR SCIENCE MONTHLY. 



passed through the vapor, loud musical tones were in each case ob- 

 tained. These are known to be the most highly absorbent vapors 

 which my experiments revealed. Chloroform and bisulphide of carbon, 

 on the other hand, are known to be the least absorbent, the latter 

 standing near the head of diathermanous vapors. The sounds ex- 

 tracted from these two substances were usually weak and sometimes 

 barely audible, being more feeble with the bisulphide than with the 

 chloroform. With regard to the vapors of amylene, iodide of ethyl, 

 iodide of methyl and benzol, other things beings equal, their power to 

 produce musical tones appeared to be accurately expressed by their 

 ability to absorb radiant heat. 



It is the vapor, and not the liquid, that is effective in producing 

 the sounds. Taking, for example, the bottles in which my volatile 

 substances are habitually kejDt, I permitted the intermittent beam to 

 impinge upon the liquid in each of them. No sound was in any case pro- 

 duced, while, the moment the vapor-laden space above an active liquid 

 was traversed by the beam, musical tones made themselves audible. 



A rock-salt cell filled entirely with a volatile liquid, and subjected 

 to the intermittent beam, produced no sound. This cell was circular 

 and closed at the top. Once, while operating with a highly atherma- 

 nous substance, a distinct musical note was heard. On examining the 

 cell, however, a small bubble was found at its top. The bubble was 

 less than a quarter of an inch in diameter, but still sufficient to pro- 

 duce audible sounds. When the cell was completely filled, the sounds 

 disappeared. 



It is hardly necessary to state that the pitch of the note obtained in 

 each case is determined by the velocity of rotation.' It is the same as 

 that produced by blowing against the rotating disk and allowing its 

 slits to act like the perforations of a siren. 



Thus, as regards vapors, prevision has been justified by experi- 

 ment. I now turn to gases. A small flask, after having been heated 

 in the spirit-lamp so as to detach all moisture from its sides, was care- 

 fully filled with dried air. Placed in the intermittent beam it yielded 

 a musical note, but so feeble as to be heard only with attention. Dry 

 oxygen and hydrogen behaved like dry air. This agrees with my 

 former experiments, which assigned a hardly sensible absorption to 

 these gases. When the dry air was displaced by carbonic acid, the 

 sound was far louder than that obtained from any of the elementary 

 gases. When the carbonic acid was displaced by nitrous oxide, the 

 sound was much more forcible still, and, when the nitrous oxide was 

 displaced by olefiant gas, it gave birth to a musical note which, when 

 the beam was in good condition and the bulb well chosen, seemed as 

 loud as that of an ordinary organ -pipe.* We have here the exact order 



* With conjugate mirrors, the sounds with olefiant gas are readily obtained at a dis- 

 tance of twenty yards from the lamp. I hope to be able to make a candle-flame effective 

 in these experiments. 



