90 PHYSIOLOGY OF LIFE. 



as mere iron. By the perfect equality of the dimensions, 

 the magnetism of the earth appears, as it were, perplexed 

 and doubtful. Now, then attach a second cube of iron 

 to the first, and the instantaneous act of the iron on the 

 magnetic needle will make it manifest that with the length 

 thus given, the magnetic influence is given at the same 

 moment. 



That electricity, on the other hand, does not act in 

 length merely, is clear, from the fact that every electric 

 body is electric over its whole surface. But that elec- 

 tricity acts both in length and breadth, and only in length 

 and breadth, and not in depth ; in short, that the (so- 

 called) electrical fluid in an electrified body spreads over 

 the whole surface of that body without penetrating it, or 

 tending ad intra, may be proved by direct experiment. 

 Take a cylinder of wood, and bore an indefinite number 

 of holes in it, each of them four lines in depth and four 

 in diameter. Electrify this cylinder, and present to its 

 superficies a small square of gold-leaf, held to it by an 

 insulating needle of gum lac, and bring this square to an 

 electrometer of great sensibility. The electrometer will 

 instantly show an electricity in the gold-leaf, similar to 

 that of the cylinder which had been brought into contact 

 with it. The square of gold-leaf having thus been dis- 

 charged of its electricity, put it carefully into one of the 

 holes of the cylinder, so, namely, that it shall touch only 

 the bottom of the hole, and present it again to the elec- 

 trometer. It will be then found that the electrometer 

 will exhibit no signs of electricity whatsoever. From this 

 it follows, that the electricity which had been communi- 

 cated to the cylinder had confined itself to the surface. 



