NATURAL PHILOSOPHY. 189 



tube is some six feet long, by one and a half inches in diameter, and the 

 flame three quarters of an inch in height. The mechanism employed to 

 give rotation to the jet consists of a grooved wheel connected by a band with 

 a small pulley. Into the latter the supply-pipe enters from below by a 

 smooth gas-light joint, which allows the pulley freely to revolve. The jet- 

 pipe, secured to the middle of the upper face of the pulley, tapers to the 

 extremity, and rising to the height of six or eight inches, is elbowed near 

 the top, so as to give the flame, when revolving, an orbit of nearly an inch in 

 diameter. When the experiment is in progress, the appearance of the hori- 

 zontal portion of the jet-pipe affords incidentally a very pretty proof of the 

 intermittence of the singing flame. As each successive explosion makes 

 this part strongly visible, it assumes the aspect of a number oflrilllnnt sjwkes 

 corresponding to the subdivisions of the crown of flame; and if, to vary this 

 effect, we blacken the horizontal part of the pipe, and fasten near its outer 

 end, or where it resumes a vertical direction, a brilliant bead of glass or 

 metal, we are presented with a circle of starry points, each of which, by a 

 proper adjustment of the motion, appears to be at rest. 



(6.) The following proof of the intermitting nature of the singing flame, 

 suggested by the effects just described, is at once so simple, and so readily seen 

 at a distance, as perhaps to merit a place among useful lecture-room illustra- 

 tions. In this experiment the jet-pipe bearing the flame is held at rest in the 

 tube, and the required effect is produced by receiving the light on a circular 

 disk of thick pasteboard or of metal, some six inches in diameter, supported 

 near the tube on a horizontal axis, around which it may be revolved by the 

 impulse of the hand. The face of the disk next the tube, colored of a dead 

 black with paint or a covering of cloth, should have a narrow strip of white 

 paper fastened upon it in a radial direction, or a small circular bit of the 

 same placed near the edge. If both faces are used alternately, we may affix 

 the white bar to one and the dot to the other. 



On bringing the six feet tube down over the flame, and giving rapid mo- 

 tion to the disk, we remark that so long as the flame continues silent, the bar 

 or dot is quite invisible; but, as soon as the sound commences, the black 

 disk becomes diversified by a series of whitish images of one or other of these 

 objects arranged at equal intervals around the central point. It is scarcely 

 necessary to say, that the number of these images, as well as their apparent 

 motion or rest, will depend on the time of rotation, as compared with the 

 intervals of the explosions of the flame. Should it happen that the period of 

 one revolution of the wheel is precisely that of a certain number of the 

 explosions, neither more nor less, or that of any multiple or sub-multiple of 

 this number, the images of the bar or dot will continue in each successive 

 rotation to present themselves at the same points; but, should this relation 

 not subsist, these images will be seen to shift their places on the disk, some- 

 times appearing to advance, and at others to retreat. 



EXPERIMENTS ON THE QUALITY OF SOUND. 



The Cosmos (Paris), December 25, 18-37, describes a very curious apparatus, 

 devised by M. Scott, by means of which some very interesting experiments 

 were made in reference to the different qualities of sounds, and the cause of 

 these differences. The apparatus consists of a tube spreading out Avidely at 

 one extremity like a trumpet, and closed at the other end by a thin stretched 

 membrane, to the middle of which is attached a very light pencil. The tube 





