02 



Report of the Kew Committee. 



of his investigations in a work entitled " Sur l'Existence et sur la 

 Cause d'une Periodicite* mensuelle des Anrores Boreales." 



Three typical negatives have also been selected, in reply to Professor 

 Pickering's request, and forwarded to the Harvard College Obser- 

 vatory, to be deposited in the collection of astronomical photographs 

 being formed there by the Director. 



At the request of Professor Balfour Stewart, some measurements 

 were made by Mr. Whipple and Mr. McLaughlin, in the Library of 

 the Royal Astronomical Society, Burlington House, of Carrington's 

 original sun-spot drawings, with a view of checking the accuracy of 

 the values of solar-spotted areas determined at the Observatory in 

 1866, and published by Messrs. De La Rue, Stewart, and Loewy in 

 their " Researches on Solar Physics," second series. The work has 

 not yet been completed. 



Transit Observations. — One hundred and fourteen observations have 

 been made of sun-transits, for the purpose of obtaining correct local 

 time at the Observatory; 224 clock and chronometer comparisons 

 have also been made. 



Shelton's clock, K.O., has been used as the standard timepiece of 

 the Observatory. 



IV. Experimental Work. 



Actinometry. — Observations have been made on favourable occasions 

 with the Stewart actinometer on the Observatory lawn, and the results 

 communicated to the Meteorological Council, who defray the cost they 

 entail. Owing to the rarity at Kew of the occurrence of periods of 

 perfectly clear sky sufficient in duration for a satisfactory experiment 

 with Stewart's apparatus, the Superintendent has instituted inquiries 

 with a view to obtaining one of Professor Langley's bolometers for 

 comparison with it. : 



Solar Radiation Thermometers. — With a view of investigating the 

 causes of the differences in the readings of black bulb thermometers 

 in vacuo, the Superintendent obtained on loan from Messrs. Negretti 

 and Zambra six of these instruments constructed according to his 

 suggestions. They were after verification arranged on a stand on the 

 Observatory lawn beside the Observatory standard of reference, and 

 read daily during the summer months. The observations have been 

 discussed, and the results indicate that the discrepancies observed in 

 the readings of this class of instrument are in part to be attributed to 

 want of uniformity in the sizes of the thermometer bulbs, and also in 

 the amount of lampblack with which they are covered. 



Photo-Nephograph. — At the request of the Meteorological Council, a 

 series of experiments have been commenced with Captain Abney's 

 Photo-Nephograph, described in the Report of the Council for 1881. 



