P. E. Chase on Terrestrial Magnetism. 375 
spective amounts of motion that the two forces would produes 
if they were able to act freely for the same time. The ifficulty 
of determining the repulsion of molecular elasticity precluding 
any satisfactory use of the former measure, I employed the other;* 
and the precise accordance of the results, thus obtained, with 
the results of observation justified the correctness of the h po- 
thesis, in the same manner as the accurate computation of plan- 
_ Gravity, therefore, with the same propriety as heat, may be 
considered as ‘a ' 
manner in which the circulating electric current is excited. 
There is a species of mechanical polarity, of which I have 
never seen any notice, that is apparently produced by motions 
Tesembling those to which the air is continually subjected. It 
may be exhibited in the following ways: 
1, In the middle of a basin of dai lay . one se of 20% 
substance (floating it by corks or otherwise, if it is heavier than 
Water). After the water has become still, lift the basin carefull 
by one hand, and hold it at arm’s length. The intermittent 
Muscular action produces longitudinal vibrations, which tend to 
* Proc. Am. Phil. Soc,, ix, 284. 7 Phil. Trans. 1831. 
* Ene. Bri : “ Magnetism,” : i 
* The effect desvetasion on the magnetic needle may be shown in a rough way, 
by causing an ordinary grindstone to revolve rapidly, and bringing a compass near 
“* By Becquerel. t Plucker. 
