276 ADVANCED ELECTRICITY AND MAGNETISM. 



of glass is broken down and punctured by an electromotive of 

 95,000 volts, but the exact character of the action which takes 

 place in the glass when it is subjected to the electromotive force 

 is not a matter for consideration, nor is it necessary to consider 

 the changes which take place in the battery, for example, which 

 may be used to produce the given voltage. Simple mechanics 

 is concerned with the correlation of what may be called lump 

 effects, such as the relationship between the size of a beam and 

 the load it can carry, the size of a fly wheel and the work it can 

 do when stopped, the thickness and diameter of a boiler shell and 

 the pressure it can stand, the size of a submerged body and the 

 buoyant force which acts upon it, the size and shape of the air 

 column in an organ pipe and its number of vibrations per second, 

 the thickness of a glass plate and the electromotive force it can 

 stand, the size of a copper wire and the current it can carry with 

 a given rise of temperature and so forth. 



THE ATOMIC THEORY. The atomic theory depends upon the 

 development of more or less hypothetical conceptions of the 

 minute details of physical action. Thus the burning of hydrogen 

 is thought of as the joining together of atoms of hydrogen and 

 oxygen; a gas is thought of as made up of an enormous number 

 of particles which fly around at random and exert pressure on an 

 exposed surface by bombardment. 



The phenomena of chemical action and those physical phe- 

 nomena which have to do with the minute details of physical 

 processes have been studied heretofore almost solely on the basis 

 of the atomic theory. Thus nearly the whole of chemistry is 

 based upon the atomic theory, the kinetic theory of gases is a 

 branch of atomic theory; the theory of crystal structure is a 

 branch of atomic theory, and the atomic theory is used to a very 

 considerable extent in studying electricity and magnetism and 

 especially in the study of the discharge of electricity through 

 gases and in the study of radio-activity. 



137. Electrons and ions. The loss of electricity by a charged 

 body has long been known to be due in part to a leakage of 



