DR. EVERETT ON ATMOSPHERIC ELECTRICITY. 
359 
The value of E 2 derived from these numbers gives maxima at 10 h 28 m and 22 h 28 m , or 
an hour and forty-six minutes later than E 2 for Kew electricity. About the same 
amount of retardation can be roughly inferred either from inspection of the numbers 
themselves, or from comparison of the curve representing them with the Kew electrical 
curve (see Plate XXI.). 
Thus far we have been speaking of diurnal variations. For annual variations, taking 
the numbers in the last column of Table II. as our data, we have the following results : — 
For the first year, 
A 0 =2T4, A 1= -643, E 1= 107° 56', A 2 =-080, E 2 =257° 31'; 
for the second year, 
A 0 =2-12, Aj = -888, E 1= 102° 38', A 2 =-030, E 2 =358°26'; 
and for the two years combined, 
A 0 =2-13, Aj=*765, ^=104° 51', A 2 =-040, E 2 =279° 19'. 
The corresponding values for Windsor, N.S., derived from the numbers given in the 
earlier part of this paper under the heading “ mean of three preceding columns,” are as 
follows, the two years being combined, except for the months of February, August, and 
September, which are taken from the first year’s observations alone, from defect of com- 
plete observations in the second year. 
A 0 =3-92, Aj=-725, E 1= 63° 43', A 2 =l-014, E 2 =354° 29'. 
In order to render these results for the two places more comparable, seeing that we 
have no direct means of comparing the units employed, we shall, as we have already 
done in the comparison of monthly means, take A 0 (or mean annual potential) as our 
unit at both places. We thus obtain the following values for the two years combined : — 
Kew . . . A 1= -359, ^=104° 51', A 2 =-019, E 2 =279° 19', 
Windsor . . A 1= -185, E 1= 63° 43', A 2 =-259, E 2 =354° 29'. 
This comparison brings out the astonishing fact that while at Kew the half-yearly 
term is almost inappreciable, at Windsor its amplitude is actually greater than that of 
the annual term. As regards phase, confining our attention to the annual term, Kew is 
earlier than Windsor by about forty-two days. The semiannual term at Kew is too 
small and too fluctuating to admit of reliable comparison. 
It must be borne in mind that the Kew reductions include wet as well as fine weather, 
the only exclusions being those produced automatically by the spot of light passing out 
of range or moving too rapidly to leave a trace ; whereas, in the Windsor reductions, 
all observations taken during rain, snow, hail, sleet, fog, thunder, or lightning were 
excluded. It is assumed, however, that this difference can go but a little way towards 
explaining the great differences which we have detected in the electrical variations at 
the two places. 
I am happy to be able to state that preparations are now in progress for resuming the 
photographic registration of atmospheric electricity at Kew with new apparatus contain- 
ing all Sir William Thomson’s most recent improvements. 
