476 Dr. C. Chree : Results obtained at Kew Observatory with 



The present paper discusses the results in a more complete 

 fashion. The observations have been taken at a fixed spot 

 in the Observatory garden, and the instrument has been used 

 in an invariable way with the cover on, following it is believed 

 the original procedure approved by Elster and Geitel. 



During the observations the instrument has stood on a 

 stone pier 1*2 metres in height situated near the middle of 

 the garden, at a considerable distance from any tree or 

 building and freely exposed to the wind. The centre of the 

 dissipation cylinder is 1*45 metres above the ground. The 

 instrument has been wholly unprotected except by its own 

 cover. No one is near the instrument unless when actually 

 reading it, and when doing so the observer stands to leeward. 

 Observations have been made only when it was dry, and when 

 the wind permitted. During high winds the electroscope 

 leaves are not sufficiently stationary, and after a little 

 experience no observations were made under such conditions. 



All the observations utilised here were taken between 

 2 and 4 P.M. The regular dissipation observations were 

 preceded and followed by a leakage experiment, to deter- 

 mine how much of the apparent loss was due to defective 

 insulation. There were usually three dissipation observations, 

 each lasting 20 minutes ; the first and last being with charges 

 of the same sign, the intermediate with a charge of opposite 

 sign. If on one day there were two positive charge experi- 

 ments, then on the next day there was only one. Thus the 

 number of experiments with positive and negative charges 

 was roughly equal, and the mean time of the experiments on 

 the same day with the charges of opposite sign practically 

 coincided. The mean monthly and annual results for the 

 dissipation of positive and negative charges may thus be 

 regarded as exactly corresponding to one another. 



At the time of observation, the observer noted the amount 

 of cloud (scale to 10) and its type or types, also whether 

 the sun was shining, and if so whether brightly or otherwise. 

 He further noted the state of the atmosphere, whether clear, 

 hazy, misty, or foggy, and the direction of the wind. Most 

 of the observations were taken by Mr. E. G. Constable, the 

 senior assistant in the Meteorological department. In his 

 absence they were taken by Mr. E. Boxall, who is also an 

 experienced meteorological observer. For the purposes of 

 the present discussion, particulars have been derived from the 

 curves of the self-recording instruments as to the mean 

 values of temperature, barometric pressure, relative humidity, 

 and electric potential gradient during each afternoon's 

 observations. 



