Donati undertook to study the Aurora with reference to the mode of its extension; and he arrived at the result that the Aurora of February 4, 1872, was not observed in different regions of the earth in the same physical moment; _but everywhere at the same local hour_, as in the case of celestial phenomena, which do not share in the earth’s rotation. [Sidenote: Questions sent to Italian Consuls.] The Minister of Foreign Affairs sent a circular to all Italian Consuls, asking them the necessary questions; and in reply received reports from forty-two places in our hemisphere and from four in the southern, the places embracing in one latitude the considerable extent of 240 degrees of longitude. An epitome of the tables (in which the results are divided into three zones) is as follows:— [Sidenote: Table of results.] +---------+--------------------+----------+------------+------------+ | Zone. | Mean longitude | No. of | Mean hour | Mean hour | | | of zone. | stations.| of maximum.| of end. | +---------+--------------------+----------+------------+------------+ | Eastern | 2 hrs. 5 mins. E. | 9 | 9½ hrs. | 12¼ hrs. | | Middle | 0 hr. 20 mins. E. | 17 | 8½ hrs. | 11½ hrs. | | Western | 5 hrs. 38 mins. W. | 13 | 8¾ hrs. | 9¾ hrs. | +---------+--------------------+----------+------------+------------+ [Sidenote: Extensions of the Aurora. The Aurora passed through four periods. First period of origin, light weak. Second period, increase of intensity. Third period, continuous brightness. Fourth period, decrease.] Donati summed up the facts:—That the light phenomena of this Aurora began to show themselves in the extreme east of the southern hemisphere in Eden and Melbourne; shortly after, they were observed in the east of our hemisphere in China (but not in Japan); from China the Aurora passed over the whole of Asia and Europe, and crossed the Atlantic and the American Continent as far as California. It was invisible in Central and South America. During these immense extensions it passed through four periods. In the first (called by Donati the period of origin) the light of the Aurora was pretty weak, and spread from Shanghai to Bombay; in the second period, during which it passed on from Bombay to Taganrog, it acquired a sudden increase of intensity; in the third period (called by Donati the normal) the Aurora passed over Europe from east to west with regularity and a continuous brightness; the fourth period, that of decrease, was observed in America. The Aurora had a tendency to end earlier in reference to the local hour in the western stations than in the eastern. The acceleration on an average of the end of the phenomenon was twenty minutes for every hour of longitude. [Sidenote: Donati’s conclusions. Explanation of mode of propagation of same Aurora.]