452 THE POPULAR SCIENCE MONTHLY. 



gas presents several inconveniences. It is difficult to prepare ; it necessitates the 

 use of gas-holders, whose size may he considerable. Besides, there is some 

 danger in its use. I have therefore given uj) using hydrogen gas, and for a year 

 I have experimented on the means of applying common illuminating gas to the 

 pyrophone, which it is always easy to procure. In tlie first experiments which 

 I attempted with two flames, witli illuminating gas, in a glass tube, I was unable 

 to obtain any sound, which proved unmistakably the presence of carbon in the 

 flames. "While the sound was produced in a very clear manner with the pure 

 hydrogen gas, that is to say, without there being any solid foreign matter in the 

 flames, it was impossible to make the tube with illuminating gas vibrate, when 

 placing the flames in an identical condition. It was necessary, then, by some 

 means or other to eliminate the carbon, a result at which I arrived by dint of 

 the following method : 



" When the flame of ordinary gas is examined, and this is introduced into a 

 tube made of glass, or of any other material (metal, oil-cloth, card-board, etc.), 

 this flame is either illuminating or sounding. 



"When this flame is only illuminating, that is to say, when the air contained 

 in the tube does not vibrate, it presents a lengthened form, and is pointed at the 

 top. Besides, it swells toward the middle, and flickers on the least current of 

 air. On the contrary, when the flame is sounding, that is to say, when the 

 necessary vibrations for the production of sound are produced in the tube, its 

 form is narrow, and large at the top. While the air of the tube vibrates, the 

 flame is very steady. The carbon in a great measure is eliminated as if by some 

 mechanical process. 



" Sounding-flames proceeding from lighting gas are in eflfect enveloped in a 

 photosphere which does not exist when the flame is merely luminous. In the 

 latter case the carbon is burnt within the flame, and contributes in a great degree 

 to its illuminating power. 



"But, when the flames are sounding, the photosphere which surrounds each 

 of them contains an exploding mixture of hydrogen and oxygen which determines 

 the vibrations in the air of the tube. 



"To produce the sound in all its intensity, it is necessary and sutiicient that 

 the whole of the explosion produced by the particles of oxygen and hydrogen in 

 a given time should be in agreement with the number of vibrations which cor- 

 respond to the sound produced by the tube. 



"To put these two quantities in harmony, I have thought of increasing the 

 number of flames so as to increase also the number of the explosions from the 

 mixture of oxygen and hydrogen in the photospheres, and thus determine the 

 vibration of the air of the tube. Instead of two flames of pure hydrogen, I put 

 four, five, six, etc., jets of lighting gas in the same tube. 



" I have besides observed that the higher a flame is, the more carbon it con- 

 tains. 



" I have then immediately been obliged to diminish the height of the flames, 

 and consequently to increase the number so that the united surface of all the 

 photospheres may sufiice to produce the vibration of the air in the tube. 



"The amount of carbon contained in the whole of the small flames will al- 

 ways be much less than the quantity of carbon corresponding to the two large 

 flames necessary to produce the same sound. In this manner I have been able 

 with separated flames to obtain sounds whose tones are as clear as those pro- 

 duced by hydrogen gas. \\'hen these, flames, or rather when the photospheres 

 which correspond to these flames, are put in contact, the sound instantly ceases. 



