So POPULAR LECTURES AND ADDRESSES. 



present time have been made in the earnest 

 desire to turn the knowledge of the properties 

 of matter to some purpose useful to mankind. 



The first step toward numerical reckoning 

 of properties of matter, more advanced than the 

 mere reference to a set of numbered standards, 

 as in the mineralogist's scale of hardness, or to 

 an arbitrary trade standard, as in the Birmingham 

 wire-gauge, is the discovery of a continuously- 

 varying action of some kind, and the means of 

 observing it definitely, and measuring it in terms 

 of some arbitrary unit or scale division. But 

 more is necessary to complete the science of 

 measurement in any department ; and that is 

 the fixing on something absolutely definite as 

 the unit of reckoning, which, with reference to 

 electric and magnetic science, is the subject of 

 my lecture of this evening. 



In electricity, the mathematical theory and the 

 measurements of Cavendish, and in magnetism, 

 the measurements of Coulomb, gave, one hundred 

 years ago, the requisite foundation for a complete 

 system of measurement : and fifty years ago 



