46 THE NEW KNOWLEDGE. 



Here, we are in another world. Instruments of infinite 

 precision surround us, optical, electrical and magnetic, and 

 the whole atmosphere of the place tingles with accuracy. 

 Things are the subject of investigation, to be sure, as they 

 are in the chemical laboratory, but they are looked at in a 

 different way. The subject of the atom is as interesting 

 to the physicist as it is to the chemist; but the method of 

 attack is different. 



As a good example of this difference of method, consider 

 the subject of gases, with which we must now occupy our- 

 selves in order to discover the first clue to the One Thing 

 which is the object of our search. The chemist, of course, 

 considers mainly the chemical properties of gases, their 

 action on other bodies and the products of the action. The 

 physicist, on the contrary, considers primarily the physical 

 properties of gases; to him the particular gas involved is 

 more or less a matter of indifference, for in their physical 

 properties all gases are wonderfully alike: which is very 

 readily shown hi the very similar manner in which they ex- 

 pand and contract under the influence of pressure and heat. 



The physical property with which we are most con- 

 cerned in our search is the electrical conductivity of a gas. 

 All gases in the normal state conduct electricity to a slight, 

 but only to a very slight, degree. If the air, for example, 

 were to any marked degree a conductor, it is obvious that 

 telegraph wires would be impossible, for the electricity 

 would leak away. The air, however, does possess a very 

 slight conductivity; and this may easily be demonstrated 

 by a little instrument known as the electroscope. 



The electroscope may be made by attaching a thin strip 

 of gold leaf to a vertical, insulated brass plate. If the gold 

 leaf and brass plate be electrified, the .repulsive force be- 

 tween the portions of the same charge causes the gold leaf 



