In the quiet course of his private life there is but little on which I shall dwell. Each year saw his range narrowed more and more till at last he was confined to one floor. In an interesting paper, which he drew up in the summer of 1874, he thus describes the state of his health:-- "Some description of my present illness, and of the causes thereof, may perhaps prove useful to young persons who may be inclined to follow a career with energy beyond their strength. "My present position is this:--The ordinary state of my health does not prevent considerable enjoyment of life, provided that I take certain precautions and observe certain rules which experience has dictated, and, further, that I am not disturbed by others; but herein lies the difficulty. To control myself is easy enough, but effectually to control others is beyond my power. "Under the former head, I find that any kind of locomotion, except within certain narrow limits, invariably proves hurtful--producing pain in the head, a feeling of incapacity for self-guidance, and, if persisted in, downright vertigo--the most perfect rest during some hours being necessary to restore me to the normal state. It is more than five years since I was in a railway-carriage, and I dare not venture on a further trial, even could I get to the stations, which, with a few unimportant exceptions, are beyond my reach; my drives, even under the most favourable circumstances, being limited to twenty or, at the utmost, to twenty-five minutes. Soon after its completion I managed to reach the Holborn Viaduct; but the Thames Embankment and the new Post Office I have never seen. As to walking, a few yards to and from the carriage is all that I can attempt. In my own rooms, indeed, and in an adjoining balcony constructed for the purpose, I am able, at certain hours, neither long after nor shortly before a meal, to pace a little every day. The restriction is not owing to any lack of muscular strength, but simply to the painful effect on my head." It was, he says, so far back as the year 1839 that he could trace the first indications of this coming inability to walk. It had grown upon him till, about the year 1868, he fell into the state which he has thus described, from which he never recovered. "This is the more remarkable," he adds, "because, when a young man, I was the best walker of the brotherhood, and could 'do' my thirty miles a day for, I believe, any number of days in succession." He managed, nevertheless, for many years to dine with the Royal Society Club.