Theories of Electricity 137 



We must rapidly pass over the period following 

 Franklin, which was devoted to a more complete under- 

 standing of electrical actions and the formulation of the 

 subject of electrostatics on a quantitative and mathemat- 

 ical basis. The idea of electric fluids repelling or at- 

 tracting each other with Newtonian forces varying in- 

 versely as the square of the distance, lent itself readily 

 to a complete and satisfactory mathematical theory of 

 electrostatics. 



As the subject developed on mathematical lines, the 

 conception of the electric fluids became more and more 

 abstract, and lost all physical significance. The fluids 

 became mere mathematical figments to serve as centers 

 of forces of attraction or repulsion acting at a distance. 



The general attitude at that time has been well put by 

 J. J. Thomson: " The physicists and mathematicians who 

 did most to develop the ' fluid theories ' confined them- 

 selves to questions of this kind, and defined and ideal- 

 ized the conception of these fluids until any reference to 

 their physical properties was considered almost indel- 

 icate." 



While the eighteenth century was mainly devoted to 

 the study of electrostatics, /. e., to the study of the phe- 

 nomena of electricity at rest, and may be considered to 

 be the age of the electroscope and of the Leyden jar, 

 the nineteenth was chiefly occupied with a considera- 

 tion of the properties of the electric current, /. e., of 



