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 carefully and persistently was the sun studied by Herschel that, for the sake of clearness, it is advisable to arrange his work not in the order of time, but according to the subject he treats of. He began at an early period to watch the sun's face, and to make experiments with the view of discovering its history, past and future. Could he but read that history or even a chapter of it, he felt that he would be able to read the history of other suns as well as ours, and perhaps to lay a foundation for fellow-labourers in the same cause to build a temple to science on. He succeeded beyond his wishes, or at least his hopes.

The first thing he endeavoured to ascertain was, whether the sun was stationary or nearly stationary in the heavens. Astronomers had already discovered that its immense fiery globe had a day like our earth, that is, that it turned round on its axis precisely as the earth does. The time it takes they found to be 25d 7h 48m of our reckoning. This is the length of the sun's day. But Herschel asked if the sun had not a year as well as a day, a time—vast, immeasurable, perhaps—in which it revolves round a centre, hidden from man's knowledge, but not from man's sight, if he only knew where to look for it. Herschel looked for