Page:Proceedings of the Royal Society of London Vol 60.djvu/25

Rh in all probability, due to the haze, or opalescence, in the air which prevailed at the time. This haze, caused more by suspended and finely divided solid m atter than by precipitated moisture, undoubtedly contributed to the general sky-illumination at the time of totality. The actual gloom during this phase of the eclipse at Fundium was certainly much less than at Grenada in 1886. I t m ust not be forgotten, however, that the altitude of the sun was very different on the two occasions. At Grenada it was only about 19°: the amount of cloud was from seven to eight (overcast = 10) at the time of totality, and much of the cloud was in the neighbourhood of the sun : whereas at Fundium the sun’s altitude was 52°, and the sky was of a bluish-grey colour and practically free from cloud.

The effect of these different conditions in the sky in the neighbourhood of the disc is seen in Mr. Forbes’ measurements when compared with those of Lieutenant Douglas, at Grenada. The ten fairly concordant observations at Fundium give, as already stated, an average value of 0026 Siemens units at 1 ft. from the screen; and the value observed by Lieutenant Douglas, 15 seconds after totality, with the same photometer, although with a different lamp and galvanometer, was 0'0197 light units.

The memoir first gives reports by Mr. Fowler and Mr. Shackleton as to the circumstances under which photographs of the spectra of the eclipsed sun were taken with prismatic cameras in West Africa and Brazil respectively on April 16, 1893. These are followed by a detailed description of the phenomena recorded, and a discussion of the method employed in dealing with the photographs. The coronal spectrum and the question of its possible variation, and the wavelengths of the lines recorded in the spectra of the chromosphere and prominences, are next studied.

Finally, the loci of absorption in the sun’s atmosphere are considered. The inquiry into the chemical origins of the chromospheric and prominence lines is reserved for a subsequent memoir. The general conclusions which have been arrived at are as follows :— (1) W ith the prismatic camera, photographs may be obtained with