322 



WRITINGS OF JOSEPH HENRY. 



[1855- 



This inference from the theory can readily be proved to 

 be in accordance with the actual condition of the excite- 

 ment, by bringing into contact with the middle of the length 

 of the conductor a small carrier ball, and afterwards apply- 

 ing it to the knob of the electroscope. If the charge given to 

 the conductor be small, scarcely any electricity will be found 

 at the middle ; if however the carrier be brought into con- 

 tact with either end of the conductor, it will receive a charge 

 of such intensity as to cause the leaves to diverge widely 

 from each other. If a charge of electricity be imparted to 

 the centre of a conductor in the form of a thin circular disc 

 the fluid will be found, by a similar examination, in the 

 greatest intensity, at the outer rim. 



If we electrify a solid globe of metal, the excitement will 

 be confined to an indefinitely thin stratum just at the surface 

 of the conductor ; for if the electricity be imparted to the 



centre of the globe along a wire 

 through a glass tube, the electri- 

 cal atoms will evidently separate 

 from each other as far as possible, 

 on account of their mutual repul- 

 sion, and would continue to di- 

 verge even beyond the surface, 

 were it not that they were stopped 

 by the non-conducting air which 

 surrounds and insulates the globe. 

 That this inference is true may be 

 shown by an arrangement which 

 is exhibited in Fig. 3, in which A 

 represents a hollow metallic globe 

 insulated on a glass pillar and 

 charged with electricity. If the 

 carrier ball B be let down into 

 the interior of the globe, so as to 

 touch the inner surface and then 

 withdrawn without touching the 

 side of the hole it will be found 

 entirely free from electricity. If however it be made to 



