OF ARTS AND SCIENCES. 



251 



be detected by empirical means, and gave an empirical correc- 

 tion of the theory of Saturn. He further stated, that there are 

 some indications of the secular action of a planet within the 

 orbit of Mercury. 



Professor Levering described an experiment in electricity, 

 and continued : — 



" It is hardly necessary to remind the Academy of the two theories 

 devised more than a century since to explain the phenomena of electro- 

 statics. One of these theories, known as the theory of Dufay, attrib- 

 utes the two electrical states of a body to an excess of one or the 

 other of two distinct electrical fluids. The other theory, known as 

 the theory of Franklin, admits the existence of only a single electrical 

 fluid, and refers the two electrical states of a body to an excess or a 

 deficiency of this fluid. 



" The imponderability of the electrical fluid, the transcendent veloci- 

 ty with which it moves, the facility with which it changes the direction 

 of its motion when in full speed, and the absence of all visible signs 

 of inertia in its swift flight, are not easily to be reconciled with the 

 hypothesis of its materiality. To assert that electricity is matter, and 

 in the same breath to deny to it all the universal properties of matter, 

 is a plain confession of our ignorance. 



" Nevertheless, these theories are convenient artifices for symboliz- 

 ing the phenomena of electrical activity, and furnishing simple ex- 

 pressions for laws which otherwise could be described only by intri- 

 cate algebraical formulae. That protracted struggle between the two 

 theories, the issue of which is still so uncertain, has no longer refer- 

 ence to the question which of these theories expresses a physical re- 

 ality ; but to this other question, which of these theories may be con- 

 sidered as the best artifice for grouping together phenomena, the 

 dynamical relations of which are not yet distinctly understood. 



"The exclusive advocates of one or the other theory, not being able 

 to find an experimentum crucis among the statical facts of electricity, 

 have made their strong appeal to certain appearances observed in cur- 

 rent electricity. These are all of the same general character, but I 

 desire at this time to call attention to only a single one, namely, the 

 direction in which the little wheel, with pasteboard vanes, moves when 

 exposed to the electricity which circulates from arm to arm of the uni- 

 versal discharger. Those vvho have opposed the conclusion in favor 



