348 



Report of the Kew Committee. 



without the intervention of a chronometer. It has accordingly been 

 made the standard timepiece of the Observatory, instead of Sbelton 

 R.S. No. 35 fixed in the computing room, which has hitherto been so 

 employed. 



A redetermination has been made of the value of the scale divisions 

 of the level of the transit instrument. 



The De La Rue Micrometer has been recently employed by Dr. 

 Schuster in the measurement of his photographs of the comet 

 observed during the eclipse of last May. 



IV. Experimental Work. 



Exposure of Thermometers. — The observations, made on the lawn of 

 the Observatory, with the view of determining the relative merits of 

 different patterns of thermometer screens were discontinued in 

 November, 1881, the Wild's screen and the De La Rue portable 

 screen being dismounted and returned to the Meteorological Office. 

 The Stevenson's screen was, however, purchased by the Committee, 

 and remains standing in situ for the purpose of exhibition to visitors, 

 and also in order that occasional thermometric experiments may be 

 conducted in it. 



An exhaustive discussion of the twenty-eight months' observations 

 has been made by the Superintendent, and submitted to the Meteoro- 

 logical Council, at their request. 



It may, however, be stated here, that the results show that the obser- 

 vations of air temperature in the thermograph screen, attached to the 

 Observatory building, only differ in the daily mean from those in a 

 freely exposed Stevenson screen 4 feet above the ground by o, 4, and 

 from a similarly placed Wild's screen, 10 feet above the surface, by 

 0°'l. The extreme variations observed have, however, occasionally 

 reached several degrees. 



Glycerine Barometer. — This instrument, although still standing in 

 the Library, has not been read since December last. No results having 

 as yet been published of the comparisons made for Mr. Jordan, the 

 inventor, the Committee are unable to form any opinion of the 

 scientific value of the instrument. 



Pendulum Experiments. — The pendulum operations in progress at 

 the date of the last Report were terminated in November, 1881, by 

 Major HerscheL, R.E., and the instruments he employed (see 

 Appendix III, p. 24) were conveyed by him, first to the Royal 

 Observatory, Greenwich, and subsequently to a house near Portland 

 Place, London. Series of observations were made in both those 

 places, and it is hoped that by this means data will have been 

 obtained, which will serve to reduce to a common standard the deter- 

 minations of gravity made by Kater, Airy, Sabine, and others. 



