436 



SCIENCE. 



[N. S. Vol. II. No. 40. 



measured quantity of the gas* from the 

 gasholder through an India-rubber tube to 

 a receiver of known efiieiency and of 

 known capacity in connection with the 

 electrometer. We have not yet measured 

 how much electricity was lost in the pas- 

 sage through the India-rubber tube. It 

 was not probably nothing; and the electric 

 densitj^ of the gas before leaving the gas- 

 holder was no doubt greater, though per- 

 haps not much greater, than what it had 

 when it reached the electric receiver. 



§ 7. The efi&eiency of the electric receivers 

 used was approximately determined bj^ put- 

 ting two of them in series, with a paraffine 

 tunnel between them, and measuring by 



in each case. This assumption was approx- 

 imately justified by the results. 



§ 8. Thus we found for the efficiencies of 

 two different receivers respectively 0-77 and 

 0'31 with air electi-ified positively or nega- 

 tively by needle points; and 0'82 and 0-42 

 with carbonic acid gas electrified negatively 

 by being drawn from an iron cylinder placed 

 on its side. Each of these receivers con- 

 sisted of block tin pipe, 4 cms. long and 1 

 cm. diameter, with 5 plugs of cotton wool 

 kept in position by six discs of fine wire 

 gauze. The great difference in their effi- 

 ciency was no doubt due to the quantities 

 of cotton wool being different, or differently 

 compressed in the two. 



means of two quadrant electrometers the 

 quantity of electricity which each took from 

 a measured quantitj' of air drawn through 

 them. By performing this experiment sev- 

 eral times, with the order of the two re- 

 ceivers alternately reversed, we had data 

 for calculating the proportion of the elec- 

 tricity taken by each receiver from the air 

 entering it, on the assumption that the pro- 

 portion taken by each receiver was the same 

 * Tlie gasholder ivas 38 cms. high and 81 cms. in 

 circumference. Ten strokes of the pump raised the 

 •water inside to a lieight of 8'1 cms., so that the vol- 

 ume of air drawn through the receivers in the experi- 

 ments was 428 cubic centimetres per stroke of the 

 pump. This agrees with the measured effective vol- 

 ume of the two cylinders of the pump. 



§ 9. We have commenced and we hope 

 to continue an investigation of the efficiency 

 of electric receivers of various kinds, such 

 as block tin, brass and platinum tubes from 

 2 to 4 cms. long, and from 1 mm. to 1 cm. 

 internal diameter, all of smooth bore and 

 without any cotton wool or wire gauze filters 

 in them ; also a polished metal solid, in- 

 sulated within a paraffine tunnel. This in- 

 vestigation, made with variotis quantities 

 of air drawn through per second, has al- 

 ready given us some interesting and sur- 

 prising results, which we hope to describe 

 after we have learned more by farther ex- 

 perimenting. 



§ 10. In addition to our experiments on 



