1830-40] ROYAL ASTRONOMICAL SOCIETY 71 the Society on 1839 January u. By the long delay in reducing his observations of a Centauri he lost the priority of publication, as Bessel had announced the discovery of the parallax of 61 Cygni to the Society two months earlier. The determinations of astronomical constants referred to in the foregoing, and others published abroad, were urgently required for the reduction of the numerous observations with improved instruments at that time being made. The Cambridge Observatory was built in 1823-24, but no work of any consequence was done until Airy was given charge of it as Plumian Professor in 1828. At first he had only a transit instrument and no assistant ; but he fell to work at once, reducing the observations without delay and preparing them for the press, so that the printing actually commenced before the end of the year. The first small volume of Cambridge Observations, 1828, came out in the spring of 1829, soon after an assistant had been appointed. The observations were continued with great regularity, the planets being specially attended to ; but it was not till 1833 January that a mural circle by Troughton & Simms was ready for work. The observatory was in every way a model institution, and its publica- tions exhibited the reductions to an extent hitherto unknown, while the principle was introduced of not attempting to correct the instrumental errors mechanically, but measuring their amount and applying numerical corrections. These and other contributions to practical astronomy naturally led to Airy's being appointed Astronomer Royal on Pond's retire- ment in 1835. Pond had originally won his reputation by a paper published in the Philosophical Transactions, 1806, in which he proved that the serious errors in Maskelyne's declinations of standard stars were due to the great quadrant having become worn at the centre. At Greenwich, Pond on the whole followed in the footsteps of Maskelyne ; the mural circle ordered by the latter shortly before his death, took the place of the quadrant, and a new transit instrument came into use in 1816. No improvements were made in the methods of reduction, so that, for instance, Bradley's table of refractions continued to be used long after it had been abandoned as inaccurate everywhere else. But the observations were certainly better than Maskelyne's, as Pond took great pains to find every possible cause of error. The greatly increased staff of assistants * also enabled him to multiply the number of single results of any quantity considered to be important. Towards the end of his life the impression gained ground in London that the Observatory had fallen into a state of disrepute ; and when the appointment was offered to Airy, it was suggested to him that
- There was one assistant when he came and six when he left.
