632 EXPERIMENTAL INVESTIGATION OF THE 
8. It has been supposed by Cavallo and other 
philosophers, that all bodies, whether metallic or 
otherwise, are endowed with magnetic powers, 
which vary considerably in degrees of energy, 
whilst under the influence of, or operating on, the 
magnetic needle. But when we meet with such 
conflicting opinions as those that appear in the 
writings of philosophers so eminent in this de- 
partment of physics as Cavallo, Coulomb, Ben- 
net, Haiiy, Biot, Becquerel, and others who have 
entered this field of research, we are necessarily 
led to infer that the subject has not yet been ac- 
curately and satisfactorily determined. 
9. The beautiful experiments of M. Arago, 
and the final developement of magnetic electricity 
by Dr. Faraday, afford an ample explanation of 
nearly all those experiments in which vibrations 
of the magnetic needle, near the bodies under 
examination, were taken as evidence of their 
magnetic actions ; as well as in all those cases in 
which light needles of the bodies examined were 
vibrated under the influence of powerful magnets. 
It is reasonable to suppose, also, that thermo- 
electric currents would influence the results of 
those experiments which were made previous to 
the discovery of that branch of electricity by Dr. 
