How long was it to last? He himself began to wonder, for he had long felt his life as if ebbing away. At length he became languid, weary, and unfit for work; even the writing of a letter cost him a painful effort, and. he felt "as if to lie down and sleep were the only things worth doing." Yet shortly after, to help a Sunday-school, he wrote his 'Five Gateways of Knowledge,' as a lecture, and afterwards expanded it into a book. He also recovered strength sufficient to enable him to proceed with his lectures to the institutions to which he belonged, besides on various occasions undertaking to do other people's work. "I am looked upon as good as mad," he wrote to his brother, "because, on a hasty notice, I took a defaulting lecturer's place at the Philosophical Institution, and discoursed on the Polarization of Light.... But I like work: it is a family weakness." Then followed chronic malaise--sleepless nights, days of pain, and more spitting of blood. "My only painless moments," he says, "were when lecturing." In this state of prostration and disease, the indefatigable man undertook to write the 'Life of Edward Forbes'; and he did it, like everything he undertook, with admirable ability. He proceeded with his lectures as usual. To an association of teachers he delivered a discourse on the educational value of industrial science. After he had spoken to his audience for an hour, he left them to say whether he should go on or not, and they cheered him on to another half-hour's address. "It is curious," he wrote, "the feeling of having an audience, like clay in your hands, to mould for a season as you please. It is a terribly responsible power.... I do not mean for a moment to imply that I am indifferent to the good opinion of others--far otherwise; but to gain this is much less a concern with me than to deserve it. It was not so once. I had no wish for unmerited praise, but I was too ready to settle that I did merit it. Now, the word DUTY seems to me the biggest word in the world, and is uppermost in all my serious doings." This was written only about four months before his death. A little later he wrote, "I spin my thread of life from week to week, rather than from year to year." Constant attacks of bleeding from the lungs sapped his little remaining strength, but did not altogether disable him from lecturing. He was amused by one of his friends proposing to put him under trustees for the purpose of looking after his health. But he would not be restrained from working, so long as a vestige of strength remained. One day, in the autumn of 1859, he returned from his customary lecture in the University of Edinburgh with a severe pain in his side. He was scarcely able to crawl upstairs. Medical aid was sent for, and he was pronounced to be suffering from pleurisy and inflammation of the lungs. His enfeebled frame was ill able to resist so severe a disease, and he sank peacefully to the rest he so longed for, after a few days' illness: