H. V. Gill — Theory of Singing Flames. 179 



5th. When the flame is of such a size, and placed at such a 

 position that it is on the point of beginning to sing, it may be 

 made to begin by sounding the note proper to the tube ; a 

 sudden noise such as the clapping of the hands will sometimes 

 suffice. 



6th. The singing may be made to cease by closing one end 

 of the tube, and sometimes by a sudden noise. 



7th. Viewed in a rotating mirror the image is composed of 

 a series of tongues, each tongue being separated from the 

 others by a dark space. 



8th. When the flame is too large to begin easily, it will 

 respond to the note proper to the tube, but will only sound 

 while the external note is sounding. 



9th. The flame becomes blue and somewhat longer when it 

 sings. 



10th. Less gas is used when the flame sings than when it 

 remains silent. 



11th. If the flame be too small it will be extinguished in a 

 few seconds by the violence of the action. 



These are the chief facts which have been recounted by 

 Tyndall and others ; there are other facts known which may 

 be looked on as deductions from, those enumerated. 



In the explanation we propose it will be seen that the theory 

 of explosions, which is admitted by some even at the present 

 time, is not the correct one. All the facts we rely on have 

 been proved by actual experiment, and we make no hypothesis 

 which has not experimental as well as theoretical corroboration. 



As the spontaneous commencement is not an essential part 

 of the phenomenon, we shall first examine the flame in the 

 actual state of sounding, and shall then show how it begins. 



A consideration of the conditions of pressure of the column 

 of air in a sounding tube is the first step in our explanation. 



When a tube, open at both ends, emits a musical note, the 

 column of air divides itself up into nodes and loops or ventral 

 segments. The position of the nodes depends on the note 

 emitted, i. e., whether the tube emits the fundamental note, its 

 octave, etc. At a node there is a considerable variation of the 

 pressure, produced by the longitudinal vibration of the column 

 of air. The pressure varies from its maximum during a con- 

 densation to its minimum during a rarefaction; these two 

 conditions occurring in each complete vibration. Various 

 methods are in use for demonstrating this fact, the best known 

 being the manometric flames of Koenig. When such a flame 

 is placed at a node, and its image observed in a rotating mirror, 

 a band of light is seen from which arises a series of tongues, 

 separated by dark spaces, each tongue corresponding to a con- 

 densation and each dark space to a rarefaction. Sometimes the 



