188 ANNUAL OF SCIENTIFIC DISCOVERY. 



ods above described have failed to produce any effect. When the flame is 

 not far from the position in which it would spontaneously sini;;, the lightest 

 breathing through the- argandpipe is sufficient to briny it to the soundiny state, and 

 to maintain a clear, smooth tone. Even when the flame is large and other- 

 \visc not readily susceptible of the sonorous action, a stronger current of air 

 applied nearer to the bottom of the resonant tube will rarely fail to bring on 

 the musical vibrations. It should be mentioned that these effects can be 

 produced in a simpler, but less satisfactory manner, by using, instead of the 

 argand burner, to conduct the current, a common glass tube, bent suitably, 

 and held near the jet-pipe below the opening of the resonant tube. 



The sound familiarly observed when a flame of any kind is blown upon, 

 and especially when the air is forced into or through the flame, in the case 

 of the jet of a blow-pipe, was long ago referred by Faraday to the combus- 

 tion of an explosive mixture formed by the air and burning matter. The 

 sound produced by a bla/ing fire of wood or bituminous coal, as contrasted 

 with the silence of a flameless mass of ignited anthracite, is an obvious illus- 

 tration of the same principle. But the experiments above described show 

 the operation of this law under conditions which enable us more satisfacto- 

 rily to mark the origin of the sound and the gradations by which it accom- 

 panies the formation of the explosive mixture. 



(4.) The in ft- nniftixi/ clinrncti / of the combustion in a singing flame li.-is 

 been beautifully shown by Prof. Tyndal, by causing the liirht of the flame 

 to fall upon a revolving mirror, from which it is reflected M> as to form a 

 series of images on a distant screen. A similar resolution of the flame into 

 successive explosions is more simply exhibited by mor'my it rapid!// to and 

 fro, or better still, by giving it a steady >< rl,-iij mution within the tube. In 

 using the former method, the jet-pipe may be attached to the common gas 

 stand by a short piece of flexible hose, and passed through a ring so placed 

 as to restrict the vibrations to a range less than the diameter of the tube. A 

 sufficiently regular movement may then be given by the hand. If, now, we 

 adjust the flame in the tube, so that it will not begin to sing for some time 

 after the vibration has commenced, or until the tube is further lowered, we 

 observe at first merely the continuous band of light due to the permanence 

 of the visual impression; but, as soon as the singing commences, this band 

 becomes waved or serrated at the top, and with a proper velocity divides 

 into nearly separate columns of flame, with obscure spaces between. 



The effect is, ho\scver, far more striking when the jlame is made to revoke at 

 a uniform rate in the tube. In this case, so long as it remains silent, it pre- 

 sents the appearance of a hollow cylinder or short tube of whitish light; but 

 the moment the singing begins, the cylinder assumes a toothed form on the 

 top, resembling a brilliant crown, and divides itself into a number of narrmo 

 luminous columns, separated by bands nearly or quite deprived of lifjlit. It is 

 hardly necessary to say that the obscure spaces mark the moments in the 

 rotation when the explosions occur, and the bright ones the successive inter- 

 vals between them. With a given rate of rotation, as might be expected, 

 the number of these subdivisions is greater in a short tube than in a long one, 

 and is greater when the tube is yielding one of its harmonic notes than when 

 giving its fundamental sound. In the same tube the number of subdivisions 

 diminishes as we increase the velocity of rotation, a less number of vibra- 

 tions or explosions in this case corresponding to one revolution of the jet. 



(5.) To render the effect visible at a distance, it is, of course, necessary to 

 use a large tube and flame. It is, however, beautifully distinct when the 



