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.