us 



Report of the Keiv Committee. 



water in the cistern, a spare jet kept in readiness being screwed 0:1 

 when the other was observed to be frozen. 



Photo-heliograph. — The re- examination of the measurements of the 

 Kew sun-pictures, as noticed in the last report, was completed in 



January, and the preliminary reductions of — have been steadily carried 



R 



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

 who has been temporarily engaged for this purpose. It is expected 

 that the above reductions will be completed by the end of the present 

 year, or early in 1880. 



Mr. Marth is still engaged on the reduction to heliocentric elements 

 of the pictures from January, 1864, to April, 1870, inclusive. 



All these operations have been conducted under the direction and 

 at the expense of Mr. De La Rue. 



The eye observations of the sun, after the method of Hofrath 

 Schwabe, as described in the report for 1872, have been made on 151 

 days, in order to maintain for the present the continuity of the Kew 

 records of sun-spots. The sun's surface was observed to be free from 

 spots on 113 of those days. 



Transit Observations. — Seventy-eight observations have been made 

 of sun-transits for the purpose of obtaining correct local time at the 

 Observatory. Eighty-six clock and chronometer comparisons have also 

 been made. This work is performed by Mr. Constable. 



Extra- Observations. — The four solar-radiation thermometers and one 

 terrestrial-radiation were observed daily until the 3rd of August, when 

 all, with the exception of one black bulb thermometer, were completely 

 destroyed by the great hailstorm which occurred on that date. Since 

 then only one, the remaining black bulb, and a new terrestrial radia- 

 tion thermometer have been daily observed. 



The Campbell sunshine recorder, described in the Report for 1875, 

 continues in action, and the improved form of the instrument, giving 

 a separate record for every day of the duration of sunshine, has been 

 regularly worked throughout the year, and its curves tabulated. 



Two papers based upon these records have been read by the Super- 

 intendent before the Meteorological Society, and published in their 

 Quarterly Journal. The first, " On the Relation between the Duration 

 of Sunshine, the amount of Solar Radiation, and the Temperature 

 indicated by the Black Bulb Thermometer," printed in vol. v, p. 142, 

 shows that these three phenomena are intimately connected with each 

 other, the curves resulting from the plotting down of the daily values 

 given by the three instruments rising and falling together almost all 

 through the year. 



The second paper, published in vol. v, p. 213, on " The Duration of 

 Sunshine, Extent of Sky clouded, and the Height of the Barometer," 

 proves that at the Kew Observatory the amount of cloud varies 



