40 ROTATION OF THE EARTH. 



being liable to wear, to expansion, and to gradual 

 decomposition, it is established by statute law of 

 Great Britain, that "the length of a pendulum 

 vibrating in the ^ part of the daily rotation of 

 the earth, in a vacuum at the sea-level, and in the 

 latitude of London, at the temperature of sixty 

 degrees, shall be resorted to for the reconstruction 

 of the standard brass-measures of the realm, in 

 case of their destruction or loss." 



The unvarying velocity of the daily rotation of 

 the earth sustains a correspondingly unvarying 

 excitation of electric currents about it, with conse- 

 quent uniform electro-magnetic forces of action 

 and reaction between every particle of the mass. 

 The extent of the electro-magnetic force of grav- 

 itation consequently represents the quantity of 

 particles in a body, as ascertained by counter- 

 poising weights commonly employed for ascer- 

 taining the quantity of matter in articles of 

 merchandise. 



The unvarying force of gravitating descent of 

 one pound thirty-three thousand feet in one min- 

 ute, or thirty-three thousand pounds one foot 

 in one minute, is adopted by engineers as the 

 measure of the power of a work-horse, as esti- 

 mated in "foot-pounds," and called "one horse- 

 power." 



The foot-pound is now commonly adopted as a 

 standard unit of all motive-power, even including 

 that of heat employed for operating steam-engines, 

 as tested by Mr. Joules. The precise extent of me- 



