ELECTRICAL UNITS OF MEASUREMENT. 75 



of its elasticity. It must, therefore, be admitted, 

 that the science of strength of materials, so all- 

 important in engineering, is but little advanced, 

 and the part of it relating to the so-called hardness 

 of different solids least of all ; there being in it no 

 step toward quantitative measurement or reckoning 

 in terms of a definite unit. 



A similar confession might have been made 

 regarding electric science, as studied even in the 

 chief physical laboratories of the world, ten years 

 ago. True, Cavendish and Coulomb last century, 

 and Ampere, and Poisson, and Green, and Gauss, 

 and Weber, and Ohm, and Lentz, and Faraday, 

 and Joule, this century, had given us the mathe- 

 matical and experimental foundation for a complete 

 system of numerical reckoning in electricity and 

 magnetism, in electro-chemistry, and in electro- 

 thermodynamics ; and as early as 1858 a practical 

 beginning of definite electric measurement had 

 been made, in the testing of copper resistances, 

 insulation resistances, and electro-static inductive 

 capacities of submarine cables. But fifteen years 

 passed after this beginning was made, and resistance 



