154 HISTORY OF THE [1860-70 were presented by him to the Society, and form a notable collection of special interest on account of their bearing on the tenability of Alexander Wilson's idea (1773) of sun-spots as depressions. Lockyer's attack on the problems of solar physics, which began in this decade with the help of the spectroscope, paved the way to great advances, leading to the foundation of the Solar Physics Committee and the Observatory at South Kensington in 1879, and doubtless also in large measure to the establishment of large observatories abroad, like that at Potsdam in 1874 and at Meudon in 1876. Warren De la Rue [1815-89], who was elected President in 1864, was the eldest son of Thomas De la Rue, the founder of the eminent firm of manufacturing stationers of Bunhill Row. He became a good engineer without having received any special training, and his shrewd inventive faculty proved of great value to the firm. We owe so much to De la Rue for his early development of the application of photography to astronomy, that it is of interest to trace the history of his work. His earliest scientific papers relate to chemical and physical researches, doubtless suggested from time to time by the requirements of his firm. James Nasmyth [180890] has recorded, in his attractive reminiscences edited by Smiles in 1883, how De la Rue had visited him in 1840 to consult about mechanical appliances for a new process for the production of white lead, and had then seen the process of casting some disks of speculum metal for reflecting telescopes. " I was then busy with the casting of my 13-inch speculum. He watched my proceedings with earnest interest and most careful attention. He told me many years after, that it was the sight of my special process of casting a sound speculum that in a manner caused him to turn his thoughts to practical astronomy, a subject in which he has exhibited such noble devotion as well as masterly skill." Nasmyth cast a disk 13 inches in diameter for him, and out of it De la Rue constructed his celebrated reflector, which he set up in his garden in Canonbury, and later at Cranford. It is clear that before 1852 December, De la Rue must have worked several such mirrors. For in his notes on the figuring of specula (M.N., 13, 44), in which he describes his polishing machine, he says : . . . " I usually succeed in producing thirteen-inch mirrors, which define the planets ... in a manner rarely equalled and never surpassed by any of the refractors which I have yet had an oppor- tunity of looking through. I am, however, free to confess that they [the refractors] defined a fixed star much more satisfactorily than my best mirrors." He acknowledges his obligations both to
