1860-70] ROYAL ASTRONOMICAL SOCIETY 155 Lassell for his ready communication of his methods of manipula- tion, and to Nasmyth for many most valuable hints in fine grind- ing and polishing ; and he describes his own figurer and polisher. He set up his best mirror, of aperture 13 inches and focal length 10 feet, equatorially mounted but without clockwork, in the garden of his house in Canonbury, and with it he studied the planets and made admirable drawings of Saturn, and Mars, and Jupiter, which were published from time to time. He was elected a Fellow of the Society on 1851 March 14. This was the year in which Archer applied collodion to photography, and suggested the use of pyrogallic acid for developing the latent image. De la Rue was quick to seize upon the newly invented collodion plates, and in the autumn of 1852 he made " some successful positive lunar photographs in from ten to thirty seconds on a collodion film, by means of an equatorially mounted reflecting telescope of 13 inches aperture and 10 feet focal length, made in my workshop, the optical portion with my own hands ; and I believe I was the first to use the then recently discovered collodion in celestial photography." It was not till 1857 that De la Rue fitted suitable driving clockwork to his reflector, when he moved it to his new residence at Cranford, about twelve miles west of London. There he raised his telescope on a pier 15 feet high, and arranged a photographic laboratory beneath the floor of the dome. From that year onwards we find in our Monthly Notices brief records of the work done at his observatory ; and from them we learn that De la Rue was constantly striving to surpass his best. He obtained new and more perfect photographs of the moon, " which will be of great value in forming selenographic charts and in showing correctly the extent and direction of the moon's libration." De la Rue's admirable w r ork in establishing solar photography might possibly have come out of his own pioneering instincts without any direct external impulse. But, as a matter of fact, the actual development of the idea and its accomplishment arose out of the discovery by Schwabe, of the periodicity of sun-spots, and the subsequent discovery of the identity of the period with that of magnetic disturbances. The Kew Observatory building had been erected by King George III. for observing the transit of Venus in 1769, and after being maintained as the King's Observatory for seventy-one years it had passed, in 1842, into the management of the British Associa- tion for the Advancement of Science, and was used for research in meteorology and terrestrial magnetism and for the testing of scientific instruments. In 1856 the new photographic telescope,
