102 



Dr. C. Chree. Observations on Atmospheric 



The irregularity in r B /r A may be due in part to the slightly unsteady 

 character of the stand forming station B. The potentials at B were 

 also much the lowest, so that errors of reading were there of most 

 importance. At the highest station, F, the variations occurring in 

 the potential sometimes made accurate measurements difficult. 



6. To give a clearer idea of the degree of uniformity shown by 

 Table III, I give in Table IV the extreme and mean readings at the 

 several stations, omitting, as in Table II, occasions of negative 

 potential. 



Table IV. 

 Readings in Volts at the several Stations. 



On one exceptional day the potential at A varied from 1200 to 

 + 1290 volts in less than forty minutes; at station F it varied from 

 2424 to over +4000 volts in about the same time. 



Constancy of Ratios during the Day. 



7. Table V gives the mean values of the ratios for the forenoon 

 and afternoon observations, treated separately, during those days 

 when there were readings at both 10.30 A.M. and 4.30 P.M. The days 

 available numbered 17, 10, and 9 respectively in the second, third, 

 and fourth series of observations. The headings " A.M." and " P.M." 

 distinguish the forenoon and afternoon observations. 



In each case treated in table V the mean value of the potential for 

 the forenoon was considerably higher than that for the afternoon. 

 Thus, at station A the ratio of the forenoon to the afternoon mean 

 potential for those days only on which there were both forenoon 



