to the Government of the day. The salary was then doubled, "thirty chaldrons of coals and one hundred pounds of wax candles" were asked for, and the enclosing of the kitchen-garden! Evidently the official mind had not grasped the idea that the astronomer-royal was no longer a fortune-telling interpreter of the heavens, as Kepler had been forced to become for bread! With one assistant all-night work was barely possible![1] The instruments in use may be judged of from "An Account of the Equatorial Instrument," or "mural quadrant," given to the Royal Society in 1793, twenty years after Herschel began his labours. The precision of observation among the ancients could not be trusted to within from five to ten minutes. Tycho Brahe reduced the probable limit of error to within one minute. Hevelius in the following century brought it down to fiften or twenty seconds, and in the century after it was reduced to seven or eight seconds.[2] To entitle observations to any credit it was then felt that a probable error of more than a few seconds could not be admitted—or perhaps only a hundredth part of the errors unavoidable in the days of Hipparchus. In 1827, Sir John Herschel was able to say that he had "secured such a degree of precision that the stars cross the wire often on the very beat of the chronometer when they are expected." Clocks, transit-instruments, mural-circles may be said to have been in their infancy when Herschel began his work. He did not propose to work or measure with these as men do in an observatory. He was eager to see with a telescope; but he soon found that, if he was to do any good, he would require to
