146 ANNUAL OF SCIENTIFIC DISCOVERY. 



broken up into rings, the constantly enlarging circular form of which 

 would be due to the same cause as that which produces the enlargement 

 of the column, namely, the greater pressure of the air in the centre. 

 That this is the case will be evident on a close inspection of a single 

 ring, when it will be found to consist of a vast number of rapidly ro- 

 tating circles, arranged on a circular axis. Let us imagine a number 

 of common, circular, bone button-moulds, each with a single hole 

 through its centre, strung on a piece of wire, which is then bent in a 

 circular form. This would give a correct idea of the structure of a 

 smoke-ring ; and if we imagine, further, each of these bone moulds rota- 

 ting downward and inward, as the ring rises and expands, the resem- 

 blance would be still more complete." 



PHENOMENA OF SOUND. 

 The following is an abstract of a recent lecture before the Roval In- 



O / 



stitution, London, by Prof. Tyndall, on the " phenomena of sound : " 

 He began by showing how musical sounds can be produced by caus- 

 ing water to flow through small apertures, these sounds being probably 

 due to the viscosity of the liquid, causing it to create tremors in the or- 

 ifice. He then proceeded to consider and exemplify the phenomena of 

 resonance in open tubes, the cavity of the mouth being adduced as an 

 instance, as in the case of the jewsharp, which thereby becomes a mu- 

 sical instrument. The human voice, it was also stated, is produced by 

 a reed instrument, the reeds being vibrating membranes, which can be 

 tightened so as to vary the pitch (as has been made visible by Czer- 

 rnak's remarkable apparatus, the Iaryngos3ope). Vibrating reeds, or 

 tongues, also produce the sound in the concertina and harmonica, and 

 are also associated with organ pipes. The latter part of the lecture 

 was devoted to the consideration of the phenomena of interference, and 

 discord or dissonance, in accordance with the following principles, based 

 on the researches of Young, Wheatstone, Savart, and other philoso- 

 phers. The sonorous shocks communicated to the ear by two tuning- 

 forks slightly out of unison are termed beats, which succeed each other 

 more rapidly as the departure from perfect unison augments, their 

 number, in a given time, being equal to the difference in the number of 

 vibrations executed in that time by the sounding bodies. When the 

 beats were slow, they could be counted with ease ; but when exceeding- 

 ly rapid, they manifested themselves to the ear by the roughness which 

 they impart to the sound ; the roughness is the cause of dissonance. 

 Professor Tyndall concluded his lecture by exhibiting some of Lissa- 

 jous's remarkable acoustic experiments, by means of tuning-forks, mir- 

 rors, and the electric lamp. It having been proved that a tuning-fork 

 does not emit sound with the same intensity in all directions, and that 

 the sounds of two tuning-forks which vibrate exactly at the same rate 

 Wend together ^o as to give the impression of a single sound, it was 

 next shown that if one tuning-fork vibrate a little more rapidly than 

 the other, at certain times both forks conspire to augment the sound, 

 and at other times they act in opposition to each other. The conse- 

 quence being an intermittent effect, composed of successive periods of 

 sound and silence. When two sounds thus neutralize each other, the 

 effect is technically called interference. It was also shown how, by the 

 stifling of a portion of the vibrations of a sounding disk, we can aug- 

 ment the sonorous intensity. 



