The Aurora Borealis. By A. Angot. "The International Scientific Series."
(Kegan Paul and Co.)—The Aurora, one is thankful to say, still baffles men of science, though the study of careful observations has led to some curious results. The period of maximum auroras coincides with the sun-spot period ; there are gaps, but then again the great periods, the begin- ning of the seventeenth century and the last quarter of that century, appear to coincide, and also the twenty-eight day period, the revolution of the spots round the sun, with the in- terval between auroras. But any attempt to construct a working theory as to the terrestrial magnetism and auroras seems beset with difficulties. It seems certain that auroras seen in our latitude are two hundred miles high ! Another remarkable fact is that the lines passing through places of equal auroral display form a series of ovals. This chart, by the way, is wrongly placed. The plates are capital, and the book by no means technical, and we recommend all readers to read M. Angot's volume, which is singularly able, lucid, and impressive.
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