90 UNIVERSITY OF MISSOURI BULLETIN 



ity. They are exceedingly small compared with even the 



smallest atom, for the mass of the unit is only —^ part of 

 the mass of an atom of hydrogen and this hydrogen mass is 

 1.61 X 10'-* gram, or it takes about 6.2 x 10-^ hydrogen 

 atoms to weigh one gram. The mass of the corpuscle is about 

 lO'-'^gram. That is, it bears about the same relation to the 

 mass of a gram weight as the gram does to the mass of the 

 earth. The radius of an electron, assuming it to be a sphere, 

 has been calculated to be between lO'^^ and 10"^^ centimeter. 

 The radius of a hydrogen atom has been calculated to be 

 about 10"^ centimeter. Hence the radius of an electron is one 

 ten-thousandth of one one-hundred thousandth of an atom or 

 about the ten-millionth or one one-hundred millionths part of 

 a wave length of light. If dimensions were so magnified 

 that a wave length of light would extend from St. Louis to 

 Kansas City, an electron would be about as big as a marble. 

 Magnified in the same proportion, a foot rule would cover 

 the distance from the earth to the sun. Another comparison 

 is that the volume of a corpuscle bears to that of the atom 

 about the same relation as that of a speck of dust to the 

 volume of this auditorium. Under suitable conditions they 

 move at enormous speeds which approach in some instances 

 the velocity of light. As cathode rays the corpuscles move at 

 the rate of 60,000 miles per second. A shot from a gun 

 moves with a velocity of about 3,000 feet per second. The 

 corpuscle goes 20 miles while the cannon ball goes one foot. 

 In a second the corpuscle could go more than twice around 

 the globe. 



The fundamental property of the electron which distin- 

 guishes it from ordinary substance is that it repels another 

 electron, instead of attracting it as two pieces of substance 

 would do. When one electron is placed at a distance of one 

 centimeter in a vacuum from another electron, it repels it 

 with a force of 1.16 x 10'^^ dynes, a force which is some- 



