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of fact, or every expression of opinion, is based upon a hundred single instances like the one which is chosen, or upon a hundred concurring judgments. It is not that you are overborne by weight but convinced by character. This most important paper came at exactly the right time. It first summarizes the works of other recent observers, which, though important, had left the subject in an entirely unsatisfying condition, and then proceeds straight to the subject in hand.

The minute details, both of the general solar surface and of the extraordinarily complex spots, are one by one satisfactorily and lucidly described, with indications of the physical conditions to which they are due; and, finally, the general bearings of all this on the received solar theories are briefly set forth. We may fairly say that this paper is fundamental. It treats of a subject of which little had been accurately known, and it leaves this subject in a satisfactory and settled