Rood — Experiments on High Electrical Resistance. 289 



Bunsen burner; for two minutes the flow of the electricity 

 was stopped, but it then began again, the intervals between 

 the strokes being 8, 7, 4, 3, 3, 3 seconds. Two days after- 

 wards the experiment was repeated with a result of 10 strokes 

 in 32 seconds. Ten days later, its rate was 10 strokes in 42 

 seconds. A sealed tube of soft German glass of the same 

 length that had been carefully cleaned and heated gave 10 

 strokes in 20 seconds ; heated again for three minutes and 

 cooled, its rate was 10 strokes in 36 secpnds and on the follow- 

 ing day this had fallen to 10 in 15 seconds. Ten days after- 

 wards it gave 10 strokes in 20 seconds. These slight irregu- 

 larities are however thrown into the shade by an observation 

 made on a tube of the same kind of glass, where the resistance 

 of one-half of it was twelve times as great as that of the 

 other, and it remained in this condition for two weeks, or 

 until it was cleaned ; then the whole of the tube had the lower 

 resistance. A tube made from the glass that is now used in 

 Germany for Leyden jars, was found to have a high resistance, 

 so that the electricity did not seem to reach its farther end at 

 all. After being in contact for three-quarters of an hour with 

 a Leyden jar having a potential of 12,000 volts, at a distance 

 of 16 cm from the jar, the potential of the tube was only 600 

 volts, and an additional exposure for the same length of time 

 extended this distance only to 22 cm . At the time these experi- 

 ments were made I had not constructed a set of units of high 

 resistance, or it would have been easy to have measured the 

 resistance of these tubes in megohms when traversed by a cur- 

 rent of 12,000 volts. Later on I measured the resistance of a 

 tube of soft German glass, 2T cm in length, which had been for 

 some days in a box dried with sulphuric acid. This at first 

 proved to be 250,000 megohms, then under the influence of 

 the current it increased to 380,000 megohms. On this day the 

 hygrometer indicated 43 per cent of moisture. Some time 

 afterwards, the hygrometer indicating 53 per cent, the resist- 

 ance of the tube had fallen to 180,000 megohms. The cur- 

 rent here employed, as in all cases where actual figures are 

 given, had a potential of only 110-112 volts. 



Silk. — A double thickness of rich brown silk, 45 ccn long, 2 cm 

 broad, conducted electricity at a potential of 12,000 volts very 

 well ; the electrometer strokes began immediately, and con- 

 tinued hour after hour. A band Of white silk was then taken, 

 a meter in length and 3 0C in breadth ; the discharges were at 

 the rate of about one per second. The silk was then boiled twice 

 in water, and dried, without affecting its rate. It was then 

 boiled in alcohol and dried ; the discharges were a little slower 

 at first, one in four seconds, but the rate soon increased to one 

 in two and a half seconds. Two threads of white sewing silk 



