OBSERVATIONS OF ATMOSPHERIC ELECTRICITY. 



449 



This, however, is not very well-marked in summer, when there does 

 not seem to be a very defined relation between the two phenomena ; it is 

 almost entirely due to the winter observations. See Table IV. 



2ud. Cloud. Both summer and winter results agree in giving a direct 

 ratio between the electrical tension of the air and the cloudiness of the 

 sky ; the average tension under an almost cloudless sky being more than 

 double what it is under a completely overcast one, the observed values 

 being for the former 142 volts, and for the latter 66. See Table V. 



Table VI. — Values of Mean Daily Tension corresponding to different 

 Values of the Mean Daily Relative Humidity of the Air. 



Relative Humidity, complete saturation being 100. 



1880 



60-64 65-69 



ro-74 



75-79 



80-84 



85-89 90-94 95-99 





January 



February 



JIarch 



April 



May 



June 



July 



August 



September 



October 



November 



December 



Dec, Jan., Feb. 

 March — May 

 June — August . 

 Sept., Oct., Nov. 



March — August 

 Sept.— Feb. 



Monthly Means 

 15 



16 



7 

 5 

 6 



15 

 6 

 6 

 5 

 6 

 5 

 4 

 24 

 15 



16 



9 



4 



5 



5 



4 



4 



11 



10 



11 



14 



14 



12 



11 



3 



6 



5 



3 



6 



11 



13 



10 



15 



9 



10 



11 



4 

 6 

 2 

 5 

 6 

 10 

 10 



14 

 11 



18 



4 



4 



4 



7 



15 



18 



15 

 2 



5-2 



Semi-annual Means 



7-3 j 6-4 I 7-1 t 



— 3-0 



10-3 



9-8 



5-2 



Annual Means 

 6-5 I 6-9 I 8-1 



6-5 

 10-2 



8-2 



6-8 

 9-8 



11-8 I 2 

 ll-O I 11-4 



91 ' 110 I 10-. 



Relative Humidity. — Table VI. The different degrees of tension cor- 

 responding to varying amounts of relative humidity cannot well be deter- 

 mined. On the whole, tension rises as the moisture of the air increases, 

 being about 50 volts when the air is but half-charged with moisture, and 

 over 100 volts when at the point of complete saturation ; the variation, 

 however, is not regular, either in summer or winter, becoming much more 

 rapid as the point of saturation is approached ; this is probably due 

 principally to the high tensions always observed during the prevalence 

 of fogs. 



The Thomson electrometer at Kew, from which these results have 

 been deduced, having been subjected to necessary re-adjustment from 

 time to time since its scale- value was originallv determined, the tensions 



1881. GG 



