A "spectroheliograph," consisting of a spectroscopic and a photographic apparatus of special type, attached to the eye-end of an equatoreal twelve inches in aperture, was erected at Kenwood in March, 1891; and with its aid, Professor Hale entered upon original researches of high promise for the advancement of solar physics. Noteworthy above all is his achievement of photographing both prominences and faculæ on the very face of the sun. The latter had, until then, been very imperfectly observed. They were only visible, in fact, when relieved by their brilliancy against the dusky edge of the solar disc. Their convenient emission of calcium light, however, makes it possible to photograph them in all positions, and emphasises their close relationship to prominences. The simultaneous picturing, moreover, of the entire chromospheric ring, with whatever trees or fountains of fire chance to be at the moment issuing from it, has been accomplished by a very simple device. The disc of the sun itself having been screened with a circular metallic diaphragm, it is only necessary to cause the slit to traverse the virtually eclipsed luminary, in order to get an impression of the whole round of its fringing appendages. And the record can be extended to the disc by removing the screen, and carrying the slit back at a quicker rate, when an "image of the sun's surface, with the faculæ and spots, is formed on the plate exactly within the image of the chromosphere formed during the first exposure. The whole operation," Professor Hale continues, "is completed in less than a minute, and the resulting photographs give the first true pictures of the sun, showing all of the various phenomena at its surface."[609] Most of these novel researches were, by a remarkable coincidence, pursued independently and contemporaneously by M. Deslandres, of the Paris Observatory.[610]