1897.] and the formation of Clouds in Charged Gases. 257 



These tables show that the negative oxygen has a denser 

 cloud for equal electrification than the positive gases. It is also 

 manifest that the weight of the cloud in each case is proportional 

 to the electrification, so that there can now be no doubt that the 

 formation of the drops is an electrical phenomenon. 



21. Rough approximations can be made to the size of the 

 drops in the case of the electrified oxygen as the outline of the 

 cloud is sometimes very definite and the rate at which the cloud 

 falls can be found. It is convenient for this purpose to photograph 

 the same cloud twice, allowing three or four minutes to elapse 

 between the two exposures. By this means it is found that the 

 cloud in the positive oxygen falls at the rate of 10 mms. in three 

 minutes, and that in the negative at the rate of 14 mms. in three 

 minutes. From these observations we get the radius a of the 



drop from the equation V=- - — (Lamb, Motion of Fluids, p. 



229). Taking /a =000185 we get for the radius of the drop in 

 the negative oxygen 8 - l x 10~ 5 , and in the positive 68 x 10 -5 . 

 Dividing the weight of the drop into the weight of the cloud 

 per c.c. the number of the drops is obtained, and dividing this 

 number into the charge per c.c. the charge on each is got. Thus 

 for positive oxygen the charge on each carrier is 28 x 10~ 10 , and 

 for the negative 31 x 10~ 10 . 



22. The weight of the drops forming the cloud as found by 

 the photographic method is not accurate to more than 8 per cent. 

 The tables giving the " relative " values of the weight of the cloud 

 per c.c. to the electrification per c.c. are accurate to 4 per cent., 

 although a slight general discrepancy exists in the charges, as the 

 condenser, two concentric cylinders, which was used to standardise 

 the electrometer had no guard ring. Hence the numbers given 

 above as the charges on each carrier are not more unequal than 

 the errors of the experiments would account for, so that there is 

 nothing in this result to disprove that the oxygen carriers have 

 the actual atomic charges. The drops in the hydrogen cloud are 

 more numerous than those in the oxygen clouds for the same 

 electrification, but I must reserve for some future occasion the 

 exact estimation of the charge on the hydrogen carrier, as at 

 present it has not been found to the degree of accuracy that is 

 desirable. 



23. The clouds which are formed by electrified gases are 

 perfectly stable even in an unsaturated atmosphere, and in this 

 respect bear a close resemblance to atmospheric clouds. There 

 are other points in favour of the supposition that the condensation 

 of the atmospheric clouds is due to electrical causes: for instance, 

 it has been amply shown in the foregoing experiments that 



