4.8 A vis inertiae

at all would perform this. For where no

resistance

“ rarer than gold. Let him also tell me, how an elec-“ trie body can by friction emit an exhalation so rareand subtile, and yet so potent, as by its emission to" cause no senfible diminution of the weight of the e-" lectric body, and to be expanded through a sphere,“ whose diameter is above two feet, and yet to be able" to agitate and carry up leaf-copper, or leaf-gold, at“ the distance of above a foot from the electric body ?“ And how the effluvia of a magnet can be so rare and" subtile, as to pass through a plate of glass without any“ resistance or diminution of their force, and yet so" potent as to turn a magnetic needle beyond the“ glass.” [Opt. p. 327.]

As to the first of these instances ; gold is a denser bo-dy than iron ; and that the particles of matter from amagnet stiould pass freely , and without impinging on thedenser body, and then impinge on , and impel the partsof the rarer body, if there were no other thing thanmaterial impulse in the case, is itself impossible and con*tradictory. These particles are but dead matter, andcan only receive an impulse in one direction; and yetthey are supposed here to pass without hindrance or let,through a denser body, and seize upon a rarer body be-yond that: If this is so, I am sure it is not an effectmerely mechanical, or performed without the interven-tion of a superior cause. What should direct them sotheir passage through the denser of the two bodies, free -ly, or without striking against the parts of it, (for it lSsaid, there is no diminution of their power •,) that theymay impelly and a£l upon the parts of the less dense ?

Fof-

2