20G 



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



ELECTRIFICATION or DIFFERENT GASES BV ELECTRIFIED NEEDLE POINTS AND 

 FLAMES. ABSOLUTE EFFICIENCIES OF FILTERS ( 47-66). 



47. The arrangement shown in fig. 7 was put up to test the electrification of 

 different gases by needle points and by flames. At first we only used one electro- 

 meter, E, and one filter, AB. The filter used was a block-tin pipe 4 centims. long, 

 1 centim. bore, with two brass gauzes and one plug of cotton wool between them. 

 A large glass cylinder, C, with a removable metal roof, R, has strips of tinfoil pasted 

 on its inside and outside. These strips are kept in metallic connection with R, 

 with one terminal, M, of an electric machine, and, with the sheath of the vertical 

 electrostatic voltmeter, V, and with the sheath of the quadrant electrometer, E. 



Fig. 7. 



A pump was used for drawing the electrified gas from the cylinder, C, through the 

 electric filter, AB. By this means, calculating the effective volumes of the two 

 cylinders of the pump, we knew the volume of electrified gas that was drawn 

 through the electric filter in each experiment. Placing the cylinder, C, over water, as 

 shown in the diagram, we found that 10 strokes of the pump raised the water 

 inside to a height of 8'1 centims. The cylinder was 38 centims. high and 81 centims. 

 in circumference. Hence the volume of gas drawn through the filter was 422'8 cub. 

 centims. per stroke of the pump. This agrees with the measured effective volume of 

 the two cylinders of the pump. 



48. An electrifying wire, ww, was put inside a glass tube full of paraffin and 



