Rood — Experiments on High Electrical Resistance. 291 



part farthest from the jar had assumed its potential, provided 

 that no electricity was conducted off from it. This is not 

 true of the substances that follow ; their case is similar to that 

 of rods conducting heat and slowly attaining the stationary 

 condition. 



Jade, gutta percha, Mack sealing wax. — There was placed at 

 my disposal a fine bar of jade, 30 cm long with a square cross 

 section of 12 mm . This was simply washed in water and sun- 

 dried. Afterwards it was exposed to 12,000 volts for fifteen 

 minutes. The electricity had traversed its whole length with 

 a diminishing potential, that of the farther end being only 600 

 volts. This would have been much more than enough to have 

 furnished electrometer strokes, but the rate of travel and the 

 rate of delivery was so slow, that the electrometer was not 

 affected. The following experiment was then made with the 

 jade, and also later, with black sealing-wax and gutta percha. 

 The end of the jade in contact with the Leyden jar had of 

 coui'se a tin-foil armature to facilitate conduction from the jar 

 to the surface of the jade ; at a distance of two centimeters 

 from this armature the jade was wrapt with a strip of tin- 

 foil, and this was brought into metallic connection with the 

 electrometer placed at some distance. This arrangement 

 assumes that the electricity will leave the Leyden jar, traverse 

 two centimeters of naked jade, and then reach the electro- 

 meter by a connecting wire, and that no electricity will pass 

 through the air by convection, and reach the movable conduct- 

 ing strip of foil and hence the electrometer. This supposition 

 appeared to be practically justified by repeated experiments, 

 where the knob of the Leyden jar retained its short distance 

 from the movable armature, but was disconnected from the 

 fixed terminal armature of the jade. I repeatedly watched for 

 ten minutes at a time without finding that the disconnected 

 jar produced any effect at all on the electrometer. This fact 

 makes it possible to study cases which otherwise would offer 

 difficulty. Using two centimeters of naked jade in this way, 

 the electrometer furnished strokes needing ten seconds. 

 Using four centimeters, the time of the first stroke was not 

 20 seconds but 47 seconds, the next following stroke needing 

 54 seconds, indicating the polarization usually observed in 

 cases of surface conduction in connection with high resistance. 

 Gutta percha and black sealing wax were now treated in 

 exactly the same way ; the movable armature being at 4 cm ; 

 they both refused to affect the electrometer, but with a distance 

 of 2 cm the times needed for electrometer strokes were as fol- 

 lows : 



