Correlations between solar activity and atmospheric electricity*: Concluded

(For additional results, not given in the Abstract on page 23, the interested reader is referred to the summary of Chief Conclusions on page 186.)19. The atmospheric‐electric observations at Brussels, as shown by curves 2 and 3 of Fig. 3, were made from 1844 to 1877 with a Peltier electrometer “at noon every day,” and as Quetelet7 states, “with all the precautions which the determination of an element so difficult to measure as electricity requires.” Beginning with the middle of 1844, it would seem that the electrometer was mounted at an invariable height above the ground and protected as far as possible from disturbing influences. In calculating the mean results for any period Quetelet “avoided the use of negative values observed during abnormal periods.” While he at various times made a thorough discussion of his observations and investigated relationships between atmospheric electricity and meteorology, he does not appear to have considered, as I had been led to believe by an erroneous reference, any relationship with sun‐spottedness. If he had done so, he would probably have found difficulty in harmonizing the annual course of his results for the period 1845 to 1856 with that for the period beginning with 1856. Excepting for the irregularity in the Brussels8 annual values of P for the period 1871 to 1875, it will be seen from curves 1, 2, 6, and 7 of Fig. 3 that for the period 1855 to 1877, 22 years, increased potential gradient corresponded in general as well with increased sun‐spottedness as did increased magnetic activity (curves 6 and 7). The same fact is true with regard to the curve (No. 3) of “Average Departures of the Annual Variation of the Potential Gradient at Brussels.”