giving the required motions up or down, right or left, were designed, drawn, and overlooked by him in their minutest details. Not a screw bolt was put in—and nothing else was used to obviate the effects of damp getting a lodgment in the woodwork—without his own eye watching or directing the work. The casting of the great mirror was begun while the building of the stand was thus proceeding. He had to remove from Datchet to Clay Hall, and thence, in 1786, to Slough, before the mirror was finished, but apparatus and materials were all transferred from the one house to the other without delaying the work. So rapidly had the work been pushed forward that the stand was ready, and the mirror, "highly polished," was put in the tube in less than a year and a half. "I had the first view through it," Herschel writes, "on Feb. 19, 1787." It was not satisfactory. "By a mismanagement of the person who cast it, it came out thinner on the centre of the back than was intended, and on account of its weakness would not permit a good figure to be given to it." Twelve or fourteen men had been daily employed in grinding or polishing it by hand, for machinery did not come into use for this purpose till 1788. It was labour lost. The work had to be begun anew, and a second mirror was cast Jan. 26, 1788, nearly a twelvemonth after the first peep into the other. Fatality again! "It cracked in cooling." Three weeks after it was recast, and by Oct. 24 it was brought to such "a figure and polish" that he tried it on the planet Saturn. He was so dissatisfied with the result that he "continued to work upon it till Aug. 27, 1789, when it was tried upon the fixed stars, and found to give a pretty sharp image,"
