206 Sir G. S. Mackenzie, Bart., on the 



form rate. It will be interesting to ascertain whether mo- 

 tion communicated to solids follows a similar law in passing 

 through them. The experiments of Biot have been supposed 

 conclusive in regard to the rate of the passage of sound 

 through the substance of cast-iron pipes, in comparison with 

 the rate of transmission through the internal column of air ; 

 sound appearing to have passed through the iron ten times 

 faster than through the included air. Now, in this case, the 

 condition of the included column, being very different from 

 that of the unconfined air, we have no comparison between 

 the rate in the iron and the rate in the open air, which it is 

 of importance to know. It is obvious, that considerable re- 

 tardation of the motion of the air in a tube is effected by the 

 rough surface of the iron, and by the numerous reflections 

 it has to undergo. It might have been predicted that, owing 

 to such causes, some difference would be observed. In re- 

 spect to the rate of motion through solids, whether it be uni- 

 form under every degree of impulse, as in the case of sound 

 and air, we must leave it for future investigation, when pro- 

 per opportunities present themselves. 



If we assume that sound is something, sui generis, brought 

 out of air by a peculiar motion imparted to it by the collapse 

 of air filling a vacuum, though we cannot define what the pe- 

 culiarity is, we may trace the manner in which it affects the 

 sensorium. Let us then conceive the peculiar motion re- 

 ferred to, to be propagated in the manner of pulses or undu- 

 lations, as described by writers on acoustics. First, there is 

 a vacuum formed, and the peculiar concussion on its being 

 filled is given, and sound produced. The concussive motion 

 is communicated to the next portion of air, and by its means 

 another vacuum is formed and filled, and a second concussion 

 takes place. This is communicated to a third portion of air, 

 and so on with great rapidity, in virtue of the elasticity of 

 the air, till an impulse is given to the tympanum, and by it 

 transmitted to the air contained in the internal ear. The 

 structure of the tympanum gives it power to regulate the 

 force of concussional impressions, so as not to permit too 

 great force to be exerted on the nervous expansion within, 



