Africa on Sunday, the 16th instant, with the same 4-inch lens of 60 inches focus which was used in Egypt in 1882, in the Caroline Islands in 1883, in Granada in 1886, and in the Salut Islands in 1889. We have thus a connected series of pictures of the corona, taken as far as possible under similar conditions, extending over a period of eleven years.
Particular interest will be attached to the department of work assigned to Mr. Fowler in Africa. He photographed the spectrum of the corona, produced by placing a glass prism in front of an object-glass of six inches aperture. The peculiar advantage of this method of observing is that for each source of light of special refrangibility in the corona a distinct image of the corona will be impressed on the plate. If, for example, the coronal light was of that strictly monochromatic type of which the light of certain nebulae appears to be, then the coronal photograph as produced through the prism would represent the details of the structure in a single definite picture. If, however, as seems much more likely, the corona diffused light of two or more refrangibilities, then separate pictures of it would be obtained in distinct positions on the plate, in correspondence with each of the constituent rays. The several pictures thus obtained would be indications of the different kinds of light of which the corona was composed. So far as these various simulacra can be discriminated and interpreted they will afford indications of the material constituents of the luminous substances from which they originate. It need not be expected that these several pictures will resemble each other. If the different parts of the corona contain different elements in their constitution, as is cer-
