1858.] Remarks on Static Induction. 478 



the gold leaves ; but the proof that it is in no way excited is not 

 quite secure until a piece of uninsulated tinfoil or metal has been 

 laid loosely on the upper surface. If there be any induction across 

 the sulphur, due to the feeble excitement of the surfaces by oppo- 

 site electricities, such a process will reveal it : a second application 

 of the flame will remove it entirely. When a plate of sulphur is 

 excited on one side only, its application to the electrometer does not 

 tell at once which is the excited side. With either face upon the 

 cap the charge will be of the same kind, but with the excited side 

 downwards the divergence will be much, and the application of the 

 uninsulated tinfoil to the top surface will cause a moderate diminu- 

 tion, which will return as the tinfoil is removed ; whereas, with the 

 excited side upwards, the first divergence of the leaves will be less, 

 and the application of the tinfoil on the top will cause considerable 

 diminution. The approximation of the flame towards the excited 

 side will discharge it entirely. The application near the un excited 

 side will also seem partly to discharge it, for the effect on the elec- 

 trometer will be greatly lessened ; but the fact is, that the flame 

 will have charged the second surface with the contrary electricity. 

 When therefore the originally excited surface is laid down upon the 

 cap of the electrometer, a diminished divergence will be obtained, 

 and it is only by the after application of uninsulated tinfoil- upon 

 the upper surface that the full divergence due to the lower surface 

 is obtained. 



Being aware of these points, which are necessary to safe manipu- 

 lation, and proceeding to work with a plate of sulphur in the field of 

 induction before described, the following results are obtained : A 

 piece of uncharged sulphur being placed in the induction field parallel 

 of course to the gutta-percha and copper- plates, and retained there, 

 even for several minutes, provided all be dry and free from dust and 

 small particles, when taken out and examined by the electrometer, 

 either without or with the application of the superposed tinfoil, is 

 found without any charge. The gilt plate carrier before described, if 

 introduced in the same position and then withdrawn is found en- 

 tirely free of charge. If the sulphur plate be in place, and then 

 the carrier be introduced and made to touch the face of the sulphur, 

 then separated a small space from it, and brought stway and exam- 

 ined, it is found without any charge ; and that whether applied to 

 either one side or the other of the block of sulphur. So that any 

 of these bodies, which may have been thrown into a polarized or 

 peculiar condition whilst under the induction, must have lost that 

 state entirely when removed from the induction, and have resumed 

 their natural condition. Assuming, however, that the sulphur had 

 become electrically polarized in the direction of the lines of in- 

 duction, and that therefore whilst in the field one face was positive 

 and the other negative, the mere touching of two or three points by 

 the gold-leaf carrier would be utterly inefficient in bringing any 

 sensible portion of this charge or state away ; for though metal can 



