III. Total eclipse of the sun observed at Caroline Island, on 6th May, 1883

Owing to the representations of the Committee on Solar Physics, who communicated with the Royal Society the desirability of observing this eclipse, an expedition was organised under the auspices of the latter body. The Council of the Royal Society having requested me to draw up a report on the Total Eclipse observed at Caroline Island, I undertook the task so far as relates to the results which were obtained with the same instruments which were employed in the observations of the Total Eclipse in Egypt in 1882. Two observers, Mr. H. Lawrance and Mr. C. R. Woods, who had both taken part in the Eclipse Expedition to Egypt as assistants to Professors Lockyer and Schuster, were entrusted with the arduous duty of making the observations. The expedition was devoted entirely to photographic work, the main object being to continue the photographic observations which had been carried on in Egypt, consisting of photographs of the corona taken on very rapid plates with varying exposure, photographs of the corona taken with a slitless spectroscope (the prismatic camera), and a photograph of the corona spectrum, the image of the moon and the corona being thrown on the slit cutting the diameter of the former. There is no occasion to describe the instruments which were employed for the first two classes of observations, as they have been fully described in the previous communication to the Royal Society by Professor Schuster and myself which appears in the ‘Philosophical Transactions’ for 1884. The photographic spectroscope which was employed on this occasion differed in one detail, and in one detail only, in that the dispersion was doubled, two medium dense flint prisms of 62½° being employed instead of one prism of the same angle. The experience gained in Egypt seemed to show that, if the coronal light was equally bright in the two eclipses, the rapid plates used on both occasions would be amply adequate to secure photographs with the larger dispersion. Besides these observations several others were made, but did not meet with the success it was hoped they would have done. A photoheliograph, giving a 4-inch solar image, was attached to an equatorial mount, in addition to the wooden camera carrying a lens of 5 ft. 6 in. focus, with which the smaller-sized pictures of the corona were taken in Egypt. The pictures taken with the former though sufficiently exposed, showed that a large image could be utilised.