242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1938 



NATURE OF ELECTRICITY 



The scientific world has offered many theories regarding the nature 

 of electricity. Benjamin Franklin's single-fluid theory was one of the 

 first. His theory pictured a colorless, weightless, invisible fluid or 

 "electrical fire" which could permeate all matter. A normal amount 

 of this fluid caused a body to be neutral, an excess amount produced 

 a positive charge, while a deficiency gave rise to a negative charge. 

 Later theories were offered by Faraday, Maxwell, and others. It 

 remained for the discovery of the electron to give a definite basis for 

 theories and conceptions which would come nearer to satisfying the 

 inquiring mind of man. Up until 1910 or later, it was generally con- 

 ceded that no one knew anything of the nature of electricity, though 



Figure 1.— Structure of the atom Figure 2— Structure of the hydrogen 



according to Bohr. atom. 



men understood quite well many of the characteristics, properties, 

 and laws of magnetism, electric charges, and electric currents. The 

 general acceptance of the electron gave rise to new theories and con- 

 ceptions in the fields of chemistry, physics, and electricity. The 

 molecule had been long considered the smallest divisible part of mat- 

 ter, the atom the smallest division of an element, and now the electron, 

 an indivisible and fundamental electric charge, a mere speck of elec- 

 tricity, became a part of the atom. Science gave the electron a mate, 

 a proton, or a positively charged particle having the same charge as 

 the electron but a mass 1,834 times as large. Then these two funda- 

 mental building blocks, the electron and the proton, became the basis 

 of all chemical elements. The difference between the elements was 

 determined by the number of pairs (electron and proton) going to 

 constitute the atom. Bohr furnished a mechanical model or picture 

 to show the structure of the building blocks within the atom. This 

 model (fig. 1) envisions a structure like a small solar system having 

 a nucleus surrounded by one or more particles moving in orbits. The 

 nucleus has a positive charge and contains all of the protons in the 

 atom. It may also contain a part of the electrons, with the remainder 

 of the electrons moving in orbits about this nucleus. The hydrogen 



