214 LORD KELVIN, DR. M. MACLEAN, AND MR. A. GALT, ON THE 



sulphuric acid in a WOULFF bottle. The electrification which we obtained in this 

 way, with the machine at 10,000 volts, was very large, the greatest deflection being 

 500 divisions in one stroke of the pump. This indicates an electric density in the air 

 of the glass cylinder, of 22 X 10~ 4 C.G.S. electrostatic, which is about six times as 

 great as that obtained by electrified needle points ( 23). This electric density was 

 got for both positive and negative electrification. 



66. We next tried the effect of the insulated hydrogen flame alone, without 

 working the electric machine, and we found that when the height of the liquid rising 

 in the long, open glass tube of the WOULFF bottle was not more than about 

 10 centims. above the level of the liquid in the bottle, there was a small negative 

 electrification. When the liquid rose to a greater height than 10 centims. in the 

 tube (indicating that the gas was issuing at a greater pressure to feed the flame), the 

 electrification was positive. On one occasion, the positive electrification produced 

 by the name was 0'84 X 10~* C.G.S. electrostatic unit per cub. centim. of the 

 air which carried the electricity to the filter. This was the greatest effect obtained 

 from the flame without electrification by the machine, and the height of the liquid in 

 the tube of the WOULFF bottle was 14'5 centims. 



The hydrogen gas, when not burning, gave no electrification at any pressure up to 

 26 centims. of water. 



PLATINUM TUBE HEATED EITHER BY A GAS FLAME OR BY AN ELECTRIC 



CURRENT ( 67). 



67. Through the kindness of Mr. E. MATTHEY, we have been able to experiment 

 with a platinum tube 96 centims. long and 1 millim. bore. It was put in between 

 the glass cylinder, C, and the filter, AB, in the apparatus of fig. 7. The other filter, 

 A'B', was not used in these experiments. The platinum tube was heated either by a 

 gas flame or an electric current. When the tube was cold, and non-electrified air 

 drawn through it, we found no sign of electrification by our filter and electrometer. 

 But when the tube was made red or white hot, either by gas burner applied externally 

 or by an electric current through the metal of the tube, the previously non-electrified 

 air drawn through it was found to be electrified strongly positive. To get complete 

 command of the temperature, we passed a measured electric current through 20 

 centims. of the platinum tube. On increasing the current till the tube began to be 

 at a scarcely visible dull red heat we found butl ittle electrification of the air. When 

 the tube was a little warmer, so as to be quite visibly red hot, large electrification 

 became manifest. Thus 60 strokes of the air-pump gave 45 scale divisions on the 

 electrometer (0'86 of a volt) when the tube was dull red, and 395 scale divisions 

 (7 '5 volts) when it was a bright red (produced by a current of 36 amperes). With 

 stronger currents raising the tube to white-hot temperature the electrification seemed 

 to be considerably less. The following summary may be taken as a specimen of 

 several experiments. It is a copy of our notes of an experiment made on 20th July, 

 1895: 



