the Combustion of Gases in Tubes. ^^77 



The mere clapping of the hauds^ producing an explosion, shout- 

 ing at an incorrect pitch, shaking of the tube surrounding the 

 flame, are, when the arrangements are properly made, ineffectual. 

 Each of these modes of disturbance doubtless affects the flame, 

 but the impulses do not accumulate, as in the case where the 

 note of the tube itself is struck. It appears as if the flame 

 were deaf to a single impulse, as the tympanum would probably 

 be, and like the latter, needs the accumulation of impulses to give 

 it sufficient motion. A difference of half a tone between two 

 tuning-forks is sufficient to cause one of these to set the flame 

 singing, while the other is powerless to produce this effect. 



I have said that the voice must be pitched to the note of the 

 tube which surrounds the flame ; it would be more correct to 

 say the note produced by the flame when singing. In all cases 

 this note is sensibly higher than that due to the open tube which 

 surrounds the flame ; this ought to be the case, because of the 

 high temperature of the vibrating column. An open tube, for 

 example, which, when a tuning-fork is held over its end, gives a 

 maximum reinforcement, produces, when surrounding a singing 

 flame, a note higher than that of the fork. To obtain the latter 

 note the tube must be sensibly longer. 



What is the constitution of the flame of gas while it produces 

 musical sounds ? This is the next question to which I will briefly 

 call attention. Looked at with the naked eye, the sounding 

 flame appears constant, but is the constancy real ? Supposing 

 each pulse to be accompanied by a physical change of the flame, 

 such a change would not be perceptible to the naked eye, on 

 account of the velocity with which the pulses succeed each other. 

 The light of the flame would appear continuous, on the same 

 principle that the troubled portion of a descending liquid jet 

 appears continuous, although by proper means this portion of 

 a jet can be shown to be composed of isolated drops. If we 

 cause the image of the flame to pass speedily over different 

 portions of the retina, the changes accompanying the periodic 

 impulses will manifest themselves in the character of the image 

 thus traced. 



I took a glass tube 3 feet 2 inches long and about an inch 

 and a half in internal diameter, and, placing it over a very small 

 flame of olefiant gas (common gas will also answer), obtained 

 the fundamental note of the tube : on moving the head to and 

 fro, the image of the sounding flame was separated into a series of 

 distinct images; the distance between the images depended upon 

 the velocity with which the head was moved. This experiment 

 is suited to a darkened lecture-room. It was still easier to 

 obtain the separation of the images in this way, when a tube 

 6 feet 9 inches in length and a larger flame were made use of. 

 As suggested to me by a lady, to whom I had the pleasure of 



