118 TRANS. OF THE ACAD. OF SCIENCE. 



interrupted descent and ascent took place from January to 

 December, we find in 1862 some interruptions in the steps of 

 that ladder. The electricity in February, 1862, is about four 

 degrees higher than that of January, April somewhat higher 

 than March, and July is the lowest instead of September in 

 1861. These trifling irregularities may be accounted for by 

 differences in temperature and relative humidity, and by a 

 greater number of thunderstorms in 1862. January of 1862, 

 for instance, was so unusually rainy, that its relative humidity 

 too was unusually high, diminishing thus electricity. But 

 the general features of distribution of electricity throughout 

 the year are apparent in both years, and we may in that re- 

 spect divide the twelve months of each year into two or three 

 groups. Computing the months which give the highest elec- 

 tricity and those which give the lowest in each year, we find 

 that in both years the months of January, February, March, 

 April, November and December exhibit the highest, and 

 the months of May, June, July, August, September and Oc- 

 tober the lowest electricity. The first group gives 



The aggregate monthly mean of 71.5 degrees of electricity in 1861 

 and 74.6 " " " 1862 



While the second group gives 29.0 " " 1861 



and 25.7 " " " 1862 



The second group prevailed therefore in 1861, and the 1st 

 in 1862. 



Or we may divide the twelve months of each year into 

 three groups. The first group with the highest electricity is 

 formed by the months of January, February, November and 

 December; the second with a mean electricity by the months 

 of March, April, May and October; and the third with the 

 lowest electricity by the months of June, July, August and 

 September. 



The aggregate monthly mean of 



The first group in 1861 is 52.9— in 1862, 54.6 

 The second " " 33.5 " 35.2 



The third " " 14.1 " 10.5 



Thus in 1861 the third group prevailed, and in 1862 the 

 first and second. But these differences are so well balanced 

 throughout the year, that the mean of the whole year in 

 lM'tl and in 1862 is exactly the same, namely, 8.4. Such an 

 identity in the yearly result, even to decimals, is of course 

 not to be expected every year; but it seems to prove, at 

 least, that the yearly mean of electricity is as constant as 

 that of temperature, of relative humidity, and of atmospheric 

 pressure. 



The third table, showing the daily periodicity of atmos- 

 pheric electricity, confirms the daily two maxima and two 

 minima of electricity as an undeniable fact. 



