56 PHYSICAL SCIENCE BK. n 



receives all that the earth sends forth for the nourish 

 ment of the heavenly bodies ; so that, of course, it 

 should be understood in this connection as material 

 rather than part. It is these earthy elements that 

 cause its fickleness and constant turmoil. Some 

 authorities believe the atmosphere to be composed 

 of separate bodies as dust is, but they are sadly in 



2 error. For there can never be internal effort in a 

 body held together in any other way than by 

 unity, 1 since the elements must be in agreement in 

 order to contribute their united strength toward the 

 tension. Now, the atmosphere, if assumed to be 

 cut up into atoms, must be dispersed. Scattered 

 elements cannot hold together as one body. But, 

 as a matter of fact, the tension of the atmosphere is 

 proved by inflated objects that will not yield to a 

 blow. It is proved, too, by weights carried up to a 

 great height merely by the support of the wind. It 

 is proved by the sound of voices sinking or swelling, 

 according to the stirring ( = vibration) of the air. For 



3 what is voice save tension of the air moulded by a 

 stroke of the tongue so as to become audible ? 

 What is all running and motion ? Are they not the 

 effects of tense air ? This it is that imparts strength 

 to the sinews, and endows the runner with his speed. 

 When, being violently stirred, it has twisted itself 

 into an eddy, it uproots trees and woods, carries 



4 aloft and shatters whole buildings. When the sea 

 lies all peaceful, the air raises it in waves. Or, to 

 descend to less violent manifestations, what song 

 can be sung without tension of breath ? Or, take 

 horns and trumpets, or those organs that by means 

 of hydraulic pressure can produce a greater volume 

 of sound than the mouth is capable of doing : is it not 



1 Or, except in a body of uniform texture. 





