WISLIZENUS — ATMOSPHERIC ELECTRICITY. 171 



nearer approach to the Sun during the colder season {perihelion) 

 might explain this regular increase of electricity during our win- 

 ter (and vice versa). But in that case our southern hemisphere 

 would in all probability be simultaneously affected, and electri- 

 cit}', like magnetism, would show there similar phenomena in 

 their summer as with us in winter. Regular and careful obser- 

 vations, continued for years in both hemispheres simultaneously, 

 with the same instruments, can decide that question. 



A third periodicity is the cyclical. In Table i the last column 

 contains the yearly means of electricity for the twelve years. We 

 find there from 1861 a gradual increase for three years, with a 

 maximum of 9.2 in 1863 ; then a gradual decrease for five years, 

 with a minimum of 2.5 in 1868 ; then an increase again for four 

 years, up to 1872 inclusive. This regular increase and decrease 

 cannot be merely accidental, but is in all probability governed 

 also by a law of periodicity. If 1873 should show a second max- 

 imum, it would establish a cycle of ten years, similar to that of 

 magnetic phenomena and of the Sun-spots. How far this cycle 

 coincides with the cyclical changes of magnetism in St. Louis I 

 was not able to ascertain, because no regular observations of mag- 

 netism are made here. Neither are any observations for Sun- 

 spots accessible to me, except those of Mr. Schwabe in Germany, 

 with a computed maximum in 1861 and the last minimum in 

 1867, diftering from mine respectively two years and one year. 

 There may be various reasons for this discrepancy. The instru- 

 ments for electrical observations still require improvement ; my 

 own observations may be sometimes defective, not having leisure 

 to make them with the regularity I could wish. Electricity is, 

 unlike magnetism and Sun-spots, often disturbed by other meteo- 

 rological phenomena, and the most important of these disturb- 

 ances, as by thunderstorms and windstorms, ought to be excluded 

 from the calculations for periodicity ; the observations of Sun- 

 spots themselves are liable to mistakes on account of the numer- 

 ous days in the year when clouds prevent observation ; all these 

 investigations are of comparatively recent date and as yet far too 

 isolated, so that, with more perfection, future observers may esta- 

 blish a still closer approximation between them. Our present 

 knowledge certainly warrants us to accept a near relationship 

 between terrestrial magnetism, Sun-spots, and atmospheric elec- 

 ticity, and by more extended observations we will reach at last 

 the final aim of all scientific research — truth. 



