356 
DR, EVERETT ON ATMOSPHERIC ELECTRICITY. 
with this I have projected the corresponding curve for Windsor, N.S. The Windsor 
observations commence four months later than those of Kew and terminate three months 
later, the time from October 1862 to May 1864 being common to both. In order to 
ensure a fair comparison, as I have no means of comparing the units in which the 
observations at the two places are stated, I have calculated the ratios of the several 
monthly means to the annual mean, and have projected these ratios. 
Inspection of the curves for the two places shows that they agree pretty well from 
January to October, but take reverse directions from October to January, the Windsor 
curve having a decided minimum in November, which is about the time of the principal 
maximum at Kew. The annual range (as a fraction of the mean annual potential) 
appears to be greater for Kew than for Windsor. The following are the ratios thus 
plotted : — 
Batio of mean monthly to mean annual potential. 
At Kew. 
At Windsor, N.S. 
1862. 
1863. 
1862. 
1863. 
June 
•770 
June 
•681 
October 
•832 
October 1*033 
July 
•773 
July .. 
•643 
November ... 
•766 
November ... *949 
August 
•836 
August 
•685 
December ... 
1-010 
December ... 1-110 
September ... 
•845 
September ... 
•854 
1863. 
1864. 
October 
•981 
October 
1-000 
January 
1-057 
January 1-125 
November ... 
1-600 
November ... 
1-390 
February ... 
1-432 
February ... ? 
December ... 
1-188 
December ... 
1-460 
March 
1-396 
March 1-416 
1863. 
1864. 
April 
1-023 
April 1-026 
January 
1-033 
January 
1-226 
May 
•796 
May -985 
February ... 
1-333 
February ... 
1-263 
June 
•720 
June -799 
March 
1-160 
March 
1-375 
July 
•755 
July *885 
April 
•920 
April 
•831 
August 
•952 
August -862 
May 
1 
•672 
May 
•549 
September ... 
•985 
The final step in the reductions has been to express the variations of electrical poten- 
tial approximately by harmonic series. Both the diurnal and the annual variations have 
been thus treated by calculating the values of the coefficients A 0 , A„ E„ A 2 , E 2 in the 
formula 
A 0 +Aj sin 360°+E^ +A 2 sin 360°+E 2 ), 
T denoting twenty-four hours in the case of diurnal, and a year in the case of annual 
variations ; and t denoting the time reckoned from noon in the former case and from the 
middle of January in the latter. 
The first step in this calculation consists in finding the values of P„ Q„ P 2 , Q 2 which 
are connected with the above-mentioned coefficients by the relations 
Pi=Ai sin E 15 Q^Aj cos E 15 P 2 =A 2 sinE 2 , Q 2 =A 2 cos E 2 . 
Commencing with the diurnal variations, we have the following values of the latter 
coefficients for the twenty-four months of observation. 
