BEPORT OF THE KEW COMMITTEE. XXXVU 



vernier reading to To'oo^th of an inch. The top slide works on the lower 

 slide, and carries a hollow axis 44 inches diameter, on which rotates hori- 

 zontally a divided circle reading to 10", and this carries a second circle on 

 the face of which are fixed four centering screws. An image intended to 

 be measured is placed on the upper circle, and is centred by means of the 

 adjusting screws ; it is then adjusted by means of the upper circle in any 

 required angular position with respect to the lower divided circle, so as to 

 bring the cross lines of the photograph in position under a fixed microscope, 

 supported on an arm from the fixed frame. By means of this instrument 

 the sun-pictures are measured so as to determine the diameter to xoVoth of 

 the radius ; the angular position of any part of a sun-spot and its distance 

 from the centre are thus readily ascertained ; or the differences of the right 

 ascension and declination with respect to the centre are as easily read off to 

 the same degree of accuracy. 



Mr. De la Rue has recently produced by his large Telescope an image of 

 a solar spot, and portion of the sun's disc, far superior to anything before 

 effected, and which leads to the hope that a new era is opened in heliography, 

 and that the resources of this Observatory might be further developed in 

 that direction. 



At the last Meeting of the Association the sum of £90 was voted for an 

 additional photographer, and of this sum £50 has been received. The Com- 

 mittee suggest that the balance of £40 be granted again at this Meeting, as 

 the full sura will be required during the ensuing year. A detailed account 

 of this expenditure will be presented in the next Annual Report- 

 Allusion was made in last Report to an instrument constructed by Prof. 

 William Thomson, of Glasgow, for determining photographically the electric 

 state of the atmosphere. This instrument has been fitted up at Kew, where 

 it has been in constant operation since the beginning of February last. It 

 has been found to answer well in a photographic point of view, and Prof. 

 Thomson has expressed himself much pleased with the results obtained. 

 The mechanical arrangements connected with the fitting up of this instru- 

 ment were devised and executed with much skill by Mr. Beckley, the 

 Mechanical Assistant, who has also recently made a working drawing of the 

 instrument for Prof. Thomson, who intends to publish a description of it. 



The arrangements made by Mr. Francis Galton, in the Observatory Park, 

 for testing sextants, and which were alluded to in last Report, are now almost 

 complete ; and six sextants sent by Captain Washington, R.N., Her Majesty's 

 Hydrographer, have been verified. 



The Observatory was honoured with a visit from His Imperial Highness 

 Prince Napoleon on the 9th of September last. His Highness expressed 

 much satisfaction at witnessing the eflScient state of the Institution. 



Application has been made to the Commissioners for the International 

 Exhibition of 1862, for a space of 40 feet by 20, in which to exhibit as 

 many as possible of the instruments in use at the Observatory, including 

 those which are self-recording. 



The Committee desire to express their thanks for a valuable addition 

 which has been made to the Library at Kew, consisting of a very large number 

 of the Greenwich publications, presented to them through the kindness of the 

 Astronomer Royal. 



It will be observed by the annexed statement that the expenditure of last 

 year has exceeded the income by about ^690 ; but as this year comprised 

 five quarters, it is hoped that the usual annual grant of £500 will cover the 

 expense until the next Meeting of the Association. 



Kew Observatory, JoHN P. Gassiot, 



"August 30, 18C1. Chairman. 



