12 



NATURE 



May 3, 1877 



simple costume of the goddesses, passes before the car of 

 Apollo, the god of the sun, while Science observes the 

 phenomenon on the earth and rtcords the results. The 

 legend is the composition of a member of the Academy 

 of Inscriptions. On the obverse of the medal is the 

 following inscription : — 



Institut De Franck 



AcAD^MiE Des Sciences 



Passage De Venus Sur Le Soleii, 



8-9 Decemher, 1874. 



THE EFFECT OF INAUDIBLE VIBRATIONS 



UPON SENSITIVE FLAMES 

 ■p^URlNG a recent visit to Birmingham my friend and 

 •L^ host, Mr. Lavvson Tait, showed me some interesting 

 experiments with one of Mr. Galton's whistles, capable of 

 yielding vibrations beyond the limit of hearing. This led 

 to the suggestion of trying a sensitive flame with these 

 whistles, and in fulfilment of my promise to select and 

 send to Mr. Tait a burner sensitive to very high notes, I 

 was yesterday led to make the following experiment, the 

 result of which is, I believe, new, and I think sufficiently 

 mteresting to put on record. A sensitive flame was ob- 

 tained just two feet high when undisturbed, but shrinking 

 down to seven inches under the influence of the feeblest 

 hiss or the clink of two coins. Adjusting the Galton 

 whistle, which Mr. Tait lent me, so as to yield its lowest 

 note, little effect was produced on the flame ; a shrill dog- 

 whistle produced a slight forking of the flame, but that 

 was all. Raising the pitch of the Galton whistle, the 

 flame became more and more agitated, until, when I had 

 nearly reached the upper limit of audibility of my left ear, 

 and had gone quite beyond the limit of my right ear, the 

 flame was still more violently affected. Raising the pitch 

 still higher, until I quite ceased to hear any sound, and 

 until several friends could likewise detect no sound, even 

 when close to the whistle, 1 was astonished to observe the 

 profound effect produced upon the flame. At every in- 

 audible puff of the whistle the flame fell fully sixteen inches, 

 and burst forth into its characteristic roar, at the same time 

 losing its luminosity, and when viewed in a moving mirror, 

 presentmg a multitude of ragged images, with torn sides 

 and flickering tongues — indicating a state of rapid, com- 

 plex, and vigorous vibration. 



Nor was this effect sensibly diminished by a distance 

 of some twenty feet from the flame. Placing the flame at 

 one end of the large lecture theatre of this college, and 

 blowing the whistle at the furthest point away, a distance 

 at least of fifty feet and more than thirty feet above the 

 flame, still the effect produced was very pronounced. 

 There can hardly be a more striking experiment. A 

 single silent and gentle puft" of air sent from the lips 

 through the whistle, nothing whatever to be heard, and 

 yet fifty feet away an effect produced that might readily 

 be seen by thousands of people. 



The extreme smallness of the amount of motion ac- 

 tually concerned in producinj; this great change in the 

 aspect ot the fl.ime is evident. For the inaudible vibra- 

 tions, having at their origin but a small amplitude, gave 

 rise to a spherical air-wave,' whi ch at a radius of flfiy 

 feet — and with the vast enfeeble ment due to this distance 

 — knocked down a two-foot flam^, though the surface 

 acted upon had an area of less than a square inch — for it 

 is only the root of the flame that picks up the wave motion. 

 Of course everything depends upon the delicately-poised 

 state into which the flame has previously to be brought. 

 It then, like a resonant jar, enters into a state of vibration 

 which appears to be synchronous with the note producing 

 the effect. By this means it may be possible, with the aid 

 of a mirror moving at a known speed, to determine the 



' I have no doubt a similar result would attend an experiment made in the 

 open air, if the air were still enough to allow it to be made. 



vibration number of these high notes, and thus with greater 

 exactitude fix the upper limit of hearing. 



The flame giving the effect here described was pro- 

 duced by coal gas contained in a holder under a pressure 

 of ten inches of water, and issuing from a steatite jet 

 having a circular orifice 0-04 inch in diameter.i 



W. F. Barreti' 



SOUND-VIBRATIONS OF SOAP-FILM 



MEMBRANES 



T^HE vibration-forms of membranes agitated by their 

 ■*• fundamental and upper tones, have usually been 

 studied by means of thin bladder or india-rubber stretched 

 on a ring or frame (see Helmholtz " Sensations of Tone," 

 chaps, iii. and v. ; Pisko, " Die Neueren Apparate der 

 Akustik," p. 75). While I was lately trying with Mr. R. 

 Knight the capabilities of various membranes of taking 

 impressions from vocal sounds for phonautographic pur- 

 poses, the idea occurred of using soap-film. This was at 

 once carried into effect by dipping the end of a lamp- 

 chimney into some soap-solution, strengthened in the 

 usual way with glycerine and a little gelatine. On 

 singing near the open end of the chimney, the 

 series of forms belonging to the various notes be- 

 came plainly visible, those produced by the upper tones 

 being as it were engine-turned in their complex sym- 

 metry, in a way to which the sand lines on so coarse a 

 material as caoutchouc can bear no comparison. To 

 exhibit these forms at a popular lecture here last nighr, 

 the light of an oxyhydrogen magic lantern was simply 

 reflected off the vibrating film upon the screen in a disc 

 of some three feet in diameter, so as to show its pat- 

 terns on a large scale when set in movement by talking, 

 singing, and playing a cornet in its neighbourhood. The 

 effects were of singular clearness and beauty. To lec- 

 turers who may use this new and easy means of making 

 the more complex sound-vibrations appreciable by the 

 eye, I would mention that by slightly thinning the soap- 

 solution, and adding a few drops of ammonia, they may 

 obtain a film more free from interference-colours, so as to 

 display the vibration-figures on an almost clear ground. 

 But if this is done, the thicker mixture should be used 

 afterwards, for the gorgeous scenic effect of the masses of 

 prismatic colour whirled hither and thither by the musical 

 vibrations. Edward B. Tylor 



Wellington, Somerset, April 20 



THE OTHEOSCOPE" 



T COMMUNICATED to the Royal Society in No- 

 •*- vember last, an account of some radiometers which 

 I had made with the object of putting to experimental 

 proof the " molecular pressure " theory of the repulsion 

 resulting from radiation. Continuing these researches I 

 have constructed other instruments, in which a movable 

 fly is caused to rotate by the molecular pressure generated 

 on fixed parts of the apparatus. 



In the radiometer, the surface which produces the 

 molecular disturbance is mounted on a fly, and is driven 

 backwards by the excess of pressure between it and the 

 sides of the containing vessel. Regarding the radiometer 

 as a heat-engine, it is seen to be imperfect in many 

 respects. The black or driving surface, corresponding to 

 the heater of the engine, being also part of the moving 

 fly, is restricted as to weight, material, and area of sur- 

 face. It must be of the lightest possible construction, or 



' The conditions necessary for obtaming the utmost sensitiveness of the 

 fl^me are described in an article I published on the subject in the Popular 

 Science Review for April, 1867. 



= On Repulsion Resulting from Radiation. Preliminary note on the 

 Otheoscope, by William Crookes, F.RS., &c. Read belore the Royal 

 Society, April 26, 1877. 



