XX 



in which he included a discussion of the Cape observations, and 

 arrived at a very similar conclusion. 



At Oxford, Stone had barely finished the work connected with his 

 great catalogue when he was nominated secretary of a committee of 

 the Royal Society, to advise the Treasury and Admiralty with 

 respect to the steps which should be taken for observation of the 

 Transit of Yenus, in 1882. An executive committee was appointed 

 by Government, in 1881, and, at the request of this committee, Stone 

 undertook the duties of " Directing Astronomer in connexion with 

 the arrangements for the observations of the Transit of Yenus, and 

 with the subsequent deduction of the results." The Radcliffe 

 Observatory was converted into a training school for the observers, 

 and Stone devoted himself, heart and soul, to the organization of the 

 various expeditions. The thoroughness with which he did this work, 

 and the great labour which he gave to it, are only fully known to 

 those who were connected with the expeditions. Stone's report, 

 which is attached to that of the executive committee and published 

 in a Parliamentary Blue Book, was issued in 1887. It gives a 

 detailed precis cf all the observations, and derives from the obser- 

 vations of various classes of contact different values of the solar 

 parallax. 



From the ' Report of the Council of the Royal Astronomical Society 

 for February, 1888,' the adopted value of the solar parallax from 

 Stone's discussion of the British Transit of Yenus observations, 

 appears to be 



8-832" ± 0-024". 



In 1883, Stone communicated to the Royal Society a paper 

 entitled " The principal Cause of the large Errors at present existing 

 between the positions of the Moon, deduced from Hansen's Tables 

 and Observation, and the Cause of an apparent Increase in the 

 secular acceleration in the Moon's Mean Motion required by Hansen's 

 Tables, or of an apparent Change in the time of the Earth's Rota- 

 tion." 



This was soon followed by a communication to the Royal Astro- 

 nomical Society of a paper entitled u On the Change of the Length 

 of the Tabular Mean Solar Day which takes place with every Change 

 in the adopted value of the Sun's Mean Sidereal Motion." 



Stone's contention was that by the adoption of Le Yerrier's Tables 

 of the Sun in the ' Nautical Almanac ' of 1864, and in subsequent 

 editions of the same work, for the computation of the sun's longitude 

 and the sidereal time at mean noon, instead of Carlini's tables, pre- 

 viously employed for this purpose, a per saltum change was made in 

 the unit of time used by astronomers, the original and cumulative 

 effect of which, from 1864, was to change by twenty-seven seconds 



