i 12 HERSCHEL AND HIS WORK 



giving thr 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. Tin- 

 casting of the great mirror was begun whil- tin 

 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, hut .1]. p.ii.it us 

 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 t he- 

 first view through it," Herschel writes, " on Feb. 19, 

 1787." It was not satisfactory. "By a mismanage- 

 ment 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 cool- 

 ing." 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," 



