ASTRONOMY. 417 



taken on 200 days, and 339 plates have been selected for preservation. 

 The sun's disk was free from spots on seven days; and, siDce the extra- 

 ordinary outburst of last November, the sun has been comparatively 

 quiescent. The astronomer royal proposes soon to employ a modi tied 

 photo-heliograph for this work, so as to obtain photographs of the sun 

 8 inches in diameter instead of 4. The measurement of a large number 

 of Indian and other photographs of the sun, required to fill gaps in the 

 Greenwich series, has been completed, these photographs having been 

 received from the Solar physics committee. 



The course of the magnetic observations has remained the same as in 

 former years. Improvements have been made in the methods of photo- 

 graphic registration. There has been considerable magnetic activity 

 during the year. The disturbances of November last are to be detailed 

 graphically in the " Greenwich magnetic results for 1882." Particulars 

 of magnetic disturbances are regularly commuuicated to the Colliery 

 Guardians newspaper, for the information of mining surveyors. 



The mean temperature of 1882 was 49°.0 or 0°.l lower than the average. 

 The highest air temperature was 81°.0, on August 6, and the lowest, 

 22°.2, on December 11. The mean daily motion of the air was 306 miles, 

 27 miles greater than the average. The greatest daily motion was 758 

 miles, on November 4, and the least, 30 miles, on December 11. The 

 greatest hourly velocity was 04 miles, October 24. The number of hours 

 of bright sunshine, as recorded by Campbell's sunshine instrument, was 

 1,245 ; that is, forty hours above the average of the five preceding years. 

 The rain-fall of 1882 was 25.2 inches, slightly above the average. 



Examination of sextant glasses, &c., at Kew. — In the Proc. Boy. Hoc. for 

 1867, Prof. Balfour Stewart described an apparatus designed and con- 

 structed by Mr. T. Cooke for the determination of the errors of gradua- 

 tion of sextants. This instrument has from that date been constantly 

 in use at the Kew Observatory, and since the introduction of certain 

 unimportant improvements has been found to work very well. 



No provision was made, however, for its employment in the determina- 

 tion of the errors of the dark shades used to screen the observer's eyes 

 when the sextant is directed to the sun or moon, and it has been found 

 that errors may exist in the shape of want of parallelism in these glasses 

 sufficiently large to seriously affect an observation accurate in other re- 

 spects. 



It has also been found that sextant makers are desirous of having 

 the shades examined before proceeding to fit them into their metal 

 mountings, and also to have the surfaces of the mirrors tested for dis- 

 tortion before making the instruments up. With a view to the accom- 

 plishment of these ends, for some time past the Kew committee have 

 undertaken to examine both dark glasses and mirrors, and to mark them 

 with a hall-mark when they are found to answer the requirements nec- 

 essary for exactitude. 

 H. Mis. 69 27 



