Donati concluded that these facts were not reconcilable with the theory of the Aurora depending on meteorological and electro-magnetic phenomena of the globe. Since, too, we have not a yearly, but a ten-yearly period of the Aurora, which coincides with that of sun-spots and terrestrial magnetism, Donati supposed that the cosmic causes of the polar lights were electro-magnetic currents between the sun and the earth. This would explain the mode of propagation of the Aurora of 4th February. Conceive an electric current going from the earth to the sun, or _vice versâ_; certain phenomena of the Aurora could only be observed in those parts of the atmosphere which have a determinate position or direction with reference to this current; and consequently these phenomena would be successively visible on the different meridians, as these meridians, by reason of the earth’s rotation, assume the same position to the current. For the Aurora to be visible certain meteorological and telluric circumstances must, however, doubtless work together with the cosmical cause. _Geographical Distribution of Auroræ (Fritz and Loomis)._ [Sidenote: Geographical Distribution of Auroræ. Prof. Fritz’s and Prof. Loomis’s line of frequency.] Professors Fritz and Loomis have investigated this subject; and Petermann’s ‘Mittheilungen,’ vol. xx. (1874), contains a paper by the former, from which it appears that the northern limit of Auroræ chosen by Professor Loomis nearly coincided, except in England, with a line of frequency in Professor Fritz’s paper. This line nearly passes through Toronto, Manchester, and St. Petersburg. Professor Loomis places it as far north as Edinburgh. On a line across Behring’s Straits, and coming down below 60° N. in America and the Atlantic, and just north of the Hebrides, to Dröntheim, and including the most northern points of Siberia, the frequency is represented by 100. [Sidenote: Within this another zone of greatest frequency and intensity.] Within this is another zone of greatest frequency and intensity, which passes just south of Point Barrow, in lat. 72° N., on the northern coast of America, and by the Great Bear Lake to Hudson’s Bay, where it reaches a latitude of 60°, then on to Nain, on the coast of Labrador, and to the south of Cape Farewell; then bending sharper to the northward, it passes between Iceland and the Faroe Islands, near to the North Cape, on by the northern ice-sea to Nova-Zembla and Cape Tschejuskin, and on just to the north of the Siberian coast to the south of Kellett Land, thence returning to Point Barrow. [Sidenote: Lines on which annually nearly the same number of Auroræ are seen.]