Report of the Keiv Committee, 



405 



time of exposure of the twin cameras, although this is apparently 

 instantaneous. 



Solar Radiation Thermometers. — The experiments with these ther- 

 mometers have been continued during the past summer months, and 

 at times as many as 8 instruments have been under observation. 



It having appeared that during the winter the vacua in certain of 

 the instruments had deteriorated either by leakage or evolution of 

 gas from the lamp-black coating of the bulbs, experiments were made 

 in the Chairman's laboratory which proved that such was the case. New 

 thermometers were made and enclosed in jackets not provided with 

 platinum electrodes ; the bulbs were also made of black glass, paving 

 the stems covered with black enamel. These, after careful exhaustion, 

 were placed under observation, but did not register temperatures 

 higher than had been previously observed. 



Advantage was taken of an offer kindly made by Professor Thorpe 

 to make solar radiation observations on his recent Eclipse Expedition 

 to Grenada, and two of the instruments were lent to him. He has now 

 returned them to the Observatory, together with copies of the readings 

 he was able to procure on the occasion. 



Electrical Anemograph. — This instrument, after a lengthened trial 

 in the Experimental House and the execution of certain minor altera- 

 tions by Mr. Kempe, has been dismounted and forwarded to the 

 Valencia Observatory by instructions of the Meteorological Council. 

 The external parts were previously put into thorough repair by 

 Mr. Munro, in order to fit the anemograph for the rough weather to 

 which it will be exposed when erected on a hill almost overlooking the 

 Atlantic. 



Dines Anemometer. — Trials have been made of two anemometers 

 constructed on a new principle by Mr. W. H. Dines, B.A. Owing, 

 however, to structural defects, both instruments broke down before 

 any final results were obtained, and were returned to the maker for 

 repair. 



Glycerine Barometer. — This instrument, having very considerably 

 deteriorated by age, was dismounted by Mr. Jordan in June, and after 

 thorough cleaning and repair by Mr. J. Steward, was again erected 

 and refilled with new fluid. 



Pendulum Experiments. — At the request of General Walker, certain 

 experiments were made with the view of ascertaining the stability of 

 the Experimental House as a site for pendulum operations. These 

 having proved that building unsuitable, a wooden erection 13 ft. X 

 9 ft. x 8 ft. has been constructed, at the desire of the Pendulum 

 Committee of the Royal Society, in the lower South Hall of the 

 Observatory, on the spot occupied in 1873 by Captain Heaviside, when 

 experimenting with the Russian pendulum. (See Report for 1873.) 



In this room it is the intention to erect the Indian Pendulum Appa- 



2 e 2 



