222 



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



In order to test if the carbonic acid gas in the lower half of the can still retained 

 any electrical charge, the connection to the filter and pump was removed from 

 aperture No. 5, at the top of the can, to No. 6 at the bottom, and the gas drawn 

 through the filter, but no electrification could be detected. We were surprised with 

 the results, and we do not see how to explain it : we expected that the stagnant 

 carbonic acid gas in the bottom of the vessel would have retained electricity as in 

 experiments of 52 and 74. 



76. Further experiments on diffusion of electricity were tried with a porous ball 

 (fig. II). The mouth of the ball was tightly closed, and through the cork passed two 

 glass tubes, one (B) projecting nearly to the bottom, the other being just through the 



Fig. 11. 



J 



cork. The ball was suspended in the metallic can, which was filled with carbonic 

 acid gas or air. The gas in the can was electrified from the insulated needle point at 

 the bottom. Meantime, a strong blast of non-electrified air from a large bellows passed 

 into, the ball by the tube, B, and out again by the other tube to the insulated standard 

 filter of block-tin tubing, 5 centims. long and 0'66 centim. bore, filled with fine brass 

 filings, the filter being connected to the insulated terminal of the quadrant electrometer. 

 There was thus an air pressure from the inside of the ball towards its outside 

 surface, and under these conditions there was no evidence on the electrometer that 

 any part of the electric charge in the carbonic acid gas or air surrounding the ball 

 had made its way against the outward pressure of air, from outside the ball into the 

 interior, and thence to the filter. This experiment was varied by removing the 

 bellows, blocking the tube, B, partially or completely, and attaching an air-pump to the 

 insulated filter at C. On working the air-pump, some of the electrified carbonic acid 

 gas or air surrounding the ball must have been drawn inside, and thence to the 



