34 EXCURSIONS ROUND LONDON* 



But it is still more astonishing, that this 

 subtile portion of the atmosphere, which 

 facilities the transmission 6f sound, is 

 composed of different species of fluids of 

 still greater tenuity ; and this is necessary: 

 for, had this subtile part of the atmosphere 

 been a homogeneous fluid, though it might 

 have transmitted one distinct undulation, 

 twenty simultaneous undulations would 

 have produced only a mere chaos. Thus, 

 for example, one stone thrown into a well, 

 produces a circle ; but several stones, 

 thrown at once into the same well, occa- 

 sion a confused mixture of indistinct figures. 



To conceive this more accurately, let us 

 suppose that some musical instruments are 

 made to produce a perfect symphony. 

 While one of the tones produces in the air, 

 in a single second, one hundred vibrations, 

 another will make a hundred and twenty- 

 five a third, a hundred and fifty. Now, 

 it is obviously impossible that the same 

 fluid should transmit at onqe one hundred, a 



hundred 



