82 



Report of the Kew Committee. 



miectrograph. — This instrument has been in almost continuous action 

 through the year under the care of Mr. Harrison. Certain improve- 

 ments in minor details, suggested by Sir "W. Thomson, have been 

 introduced from time to time. 



It has been thought desirable to make a determination of the scale 

 value of the instrument throughout the whole extent of its range. 

 The Committee not possessing a sufficiently powerful battery for the 

 purpose, the Electrometer was conveyed at Mr. De La Rue's sugges- 

 tion to his Laboratory, where a complete determination of its scale 

 value was made over the range of tension afforded by 1,200 chloride 

 of silver cells. A detailed account of the experiment was afterwards 

 laid before the Royal Society, and printed in the " Proceedings," vol. 

 xxvii, p. 356.* 



At the request of Professor Mascart, a typical set of curves, 

 illustrating the action of the Electrograph during different kinds of 

 weather, was reduced and engraved by the Pantagraph at the 

 Meteorological Office, and forwarded for his use in illustration of the 

 lectures he delivered before the Societe Meteorologique de France. 



These engravings have since been reproduced, together with notes 

 respecting the instrument, in a Report on Atmospheric Electricity, 

 drawn up by Professor Everett, for the Permanent Committee of the 

 Vienna Congress, which is about to be published by the authority of 

 the Meteorological Council. 



The late Captain R. Gr. Scott, R.E., and since his decease, Captain R. 

 Y. Armstrong, R.E., visited the Observatory and inspected the working 

 of the instrument with the view of possibly utilizing the Electro- 

 meter in the study of atmospheric electricity at the various torpedo 

 stations round the coast. 



Two Electrographs, similar in construction to the instrument at 

 Kew. have been constructed by Mr. White, of Glasgow, and after 

 examination at the Observatory, forwarded, the one to the Brussels 

 Observatory, the other to Zi-ka-Wei, China. 



PJiotohelii' graph. — The re-examination of the measurements of the 

 Kew sun-pictures, as noticed in former Reports, has been steadily 

 carried on throughout the year by Mr. Whipple, assisted by Mr. 

 M'Laughlin, who has been temporarily engaged for this purpose. 



During the year upwards of 400 pictures have been measured, and 

 it is hoped that the end of the series will be reached in the early 

 months of 1879. 



* TVith the view of rendering the indications of the instrument better adapted 

 for treatment with the Harmonic Analyser, it is in contemplation to somewhat alter 

 the existing bifilar suspension of the needle, and at the same time to adopt the 

 new insulating stand devised by Professor Mascart (" Nature," vol. xviii, p. 44) 

 which will be substituted for the present supports of the water reservoir. These 

 changes may cause a short discontinuity in the observations. 



