THE ASTRONOMICAL VIEW OF NATUEE. 369 



fixed the elementary conceptions and quantities with 

 which he operated. All his researches were comprised 

 under the very significant title " electro-dynamical mea- 

 surements." As such they remain a great monument 

 of ingenuity and unparalleled accuracy.-^ The second 



^ Gauss had, some years before 

 Weber commenced his electrical re- 

 searches, introduced the idea of an 

 absolute measure of other than 

 mechanical forces i.e., following 

 up the definition of force in the 

 Newtonian laws of motion, that it 

 is the cause which brings about a 

 change of motion, he suggested that 

 every physical force can be measured 

 by the velocity it imparts to a mov- 

 able body of measurable mass, the 

 quantity of mass being in the same 

 locality measured by its weight ; 

 and he applied this to the measure- 

 ment of magnetic forces. In ap- 

 plying the same idea to the measure- 

 ment of electric currents, Weber 

 came at once upon the circumstance 

 that the forces exerted by an elec- 

 tric current can be measured in 

 two ways viz. , by the action they 

 have upon magnets or by that 

 which they have on other electric 

 currents. Now by a familiar con- 

 ception, electricians look upon a 

 current of electricity as measur- 

 able by the quantity of electric- 

 ity which flows through a section 

 of the circuit in a given unit of 

 time, this quantity of electricity 

 being measurable in the same way 

 as Coulomb measured the action 

 at a distance of charged bodies. 

 Should it then be possible to 

 carry out this latter measurement 

 of an electric current, a comparison 

 between the electro-magnetic and 

 the known electro-static units of 

 electricity would become possible. 

 Faraday had already, in 1833 and 

 1834, made estimates of the numer- 

 ical relation of the quantity of 

 electricity in a current, measured 



VOL. I. 



by its chemical or electro-magnetic 

 effects, and of the same quantity if 

 produced by an electrical machine. 

 These estimates were more than 

 twenty years later, in 1856, reduced 

 to accurate measurements by Weber 

 and Kohlrausch. Through these 

 measurements, which confirmed the 

 enormous numbers which are re- 

 vealed when we compare electricity 

 at rest and electricity in motion, 

 Weber finished the series of ac- 

 curate measurements, reduced to 

 an absolute or mechanical standard, 

 which had been begun by Gauss in 

 1833. It was soon recognised of 

 what practical importance these 

 data must be to electricians. Ac- 

 cordingly the British Association at 

 their meeting at Manchester in 1861 

 appointed a committee, on the sug- 

 gestion and under the presidency 

 of Sir William Thomson, called the 

 " British Association Committee of 

 Electrical Standards." " This com- 

 mittee worked for nearly ten years 

 through the whole field of electro- 

 magnetic and electro-static measure- 

 ment, until in its final report, pre- 

 sented to the Exeter meeting in 

 August 1869, it fairly launched the 

 absolute system for general use " 

 (Thomson, 'Popular Lectures and 

 Addresses,' vol. i. p. 84). In recog- 

 nition of Weber's great merit in 

 first introducing this system into 

 electrical science and practice, the 

 name " Weber " had been selected 

 by Latimer Clark for the unit of 

 current. In the final fixing of the 

 units in Paris in 1881 other units 

 than those previously in use were 

 adopted, and to avoid confusion the 

 names were somewhat differently 



2 A 



