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



and freezing, and ultimate evaporation from the liquid carbonic acid in the cylinder. 

 Various experiments were tried, with the cylinder (1) lying on its side, (2) standing, 

 straight up : in both cases without any electrification of the needle points. Very 

 slight positive electrification was found with the cylinder straight up ; and very large 

 negative electrification when the cylinder was lying on its side. In the latter case, 

 the more rapid the rush of the carbonic acid gas from its cylinder, and the shorter 

 the time it was left in the glass vessel before observations were taken, the greater 

 was the electrification observed. 



TESTING EFFICIENCY OF DIFFERENT FILTERS BY USING TWO AT A TIME IN SERIES 

 AND TWO ELECTROMETERS ( 55-60, with reference to 11, 12 above). 



55. For the purpose of testing the efficiencies of various filters, two electrometers 

 were fitted up side by side, as shown in fig. 7, each with a filter of block-tin pipe, 

 4 centims. long and 1 centim. bore, containing six wire gauzes and five plugs of 

 cotton wool. These filters were put in series, with a paraffin tunnel between them 

 to insulate the one from the other. Thus the electrified air passed the second 

 receiver immediately after it passed the first. Call the one filter AB and the other 

 filter A'B' ; then, in the first experiment, the electrified gas passed in the direction 

 AB A'B', and in the second experiment it passed in the direction B'A' BA. Each 

 filter is kept metallically connected always to the same electrometer. The sensitive- 

 ness of electrometer, E, with the filter, AB, was 52 '3 divisions per volt, and 100 

 divisions per 0'154 electrostatic unit of electricity. The sensitiveness of electrometer, 

 E', with the filter, A'B', was 158'3 divisions per volt, and 100 divisions per 0'071 

 electrostatic unit of electricity. 



56. Air was electrified negatively by six needle points in the glass cylinder and 

 the pump worked at the same time with the U-tube open, so that the water did not 

 rise inside. 100 strokes of the pump gave a deflection of 160 divisions on electro- 

 meter, E, and 32 divisions on electrometer, E'. This gives 



g ( 1 = 0'246 electrostatic unit, 

 ? 2 = 0-023 



Reversing the direction of the current of air through the filters, 100 strokes of the 

 pump gave a deflection of 156 divisions on electrometer, E', and 123 divisions on 

 electrometer, E. This gives 



<?/ = O'lll electrostatic unit, 

 ft' = 0-189 

 Hence ( 12) 



n = 077 (filter AB), 

 and 



n' = 0-31 (filter A'B'). 



