past midnight, he was on the grass-plot surrounded by between fifty and sixty persons without having time for putting on proper clothing or for the least nourishment passing his lips. Among the company, I remember, were the Duke of Sussex, Prince Galitzin, Lord Darnley, a number of officers, Admiral Boston, and some ladies." This tremendous strain told on Herschel, and the result was that in the spring he became dangerously ill. Caroline tells us that on 26th February, 1807, he was so ill that even she was not allowed to see him, and until 8th March his recovery was despaired of. However, he rallied and recovered, but his health was permanently impaired. But his mind was as clear as ever, and some of his most remarkable papers were written after his illness—that of 1811, in which he developed the nebular hypothesis, and those of 1814, 1817, and 1818, on the construction of the heavens. Physically, however, he was unequal to the task of attending to his great telescopes. On 30th September, 1815, his sister recorded that "his strength is now, and has for the last two or three years, not been equal to the labour required for polishing 40-foot mirrors. And it was only by little excursions and absences from his workrooms he for some time recovered from the effects of over-exertion". During these last years, Caroline's diaries make sad reading, for they record little more than the gradual decay of health and vigour in the "best and dearest of brothers". His inability to repolish his great mirror was a bitter disappointment to him, and he became depressed and sorrowful. She afterwards recorded that "when all hopes for the return of vigour and strength necessary for resuming the unfinished task was gone, all cheerfulness and spirits had also forsaken him. . . . Every nerve of the dear man had been unstrung by over-exertion," so that "a further attempt at leaving the work complete became impossible". In 1819, before his departure for a holiday at Bath, "the last moments before he stepped
