1876

“At the door from the Front Court to the staircase of the Octagon Room (the original entrance to the Observatory as erected by Sir Christopher Wren), a small porch-shelter has been often desired. I proposed to fix there a fan-roof of quadrantal form, covering the upper flat stone of the external steps.—On a critical examination of the micrometer-screws of the Transit Circle it was found that the corrections, which range from — 1.38″ to + 0.76″, indicate considerable wear in the screws; and it was found that as much as one-hundreth part of an inch had been worn away from some of the threads. The old screws were consequently discarded, and new ones were made by Mr Simms.—The adjustment of the Spectroscope has occupied a great deal of attention. There was astigmatism of the prisms; and false light reflected from the base of the prisms, causing loss both of light and of definition. The latter defect was corrected by altering the angles, and then astigmatism was corrected by a cylindrical lens near the slit. The definition in both planes was then found to be perfect.—The number of small planets has now become so great, and the interest of establishing the elements of all their orbits so small,—while at the same time the light of all those lately discovered is very faint, and the difficulty and doubt of observation greatly increased,—that I have begun to think seriously of limiting future observations to a small number of these objects.