122 



Report of the Kew Committee. 



intervals, during periods of atmospheric disturbance, so as to de- 

 termine its relative degree of sensibility as compared with ordinary 

 mercurial instruments. 



Be La Rue Evaporation Gauge. — The Vice- Chairman of the Com- 

 mittee has devised a small evaporation gauge, by means of which the 

 water given off from a continually-wetted sheet of vegetable parch- 

 ment is measured daily. Two of these instruments, constructed by 

 Messrs. Negretti and Zambra, were set up at Kew, and their indications 

 noted every day, at 10 a.m., together with those of a Piche Evapori- 

 metre, until the end of July, when, at the request of the Meteorological 

 Council, they were transferred to the care of Mr. Shaw, who is at 

 present engaged at Cambridge in an experimental investigation on 

 hygrometry. 



Be La Rue Anemograph. — The electrical attachment to this in- 

 strument having been successfully completed after a somewhat 

 lengthy series of experiments, its registrations were discontinued and 

 the instrument was partially dismounted, in order to allow of its vane 

 being used for certain experiments now in progress with regard to the 

 working of air-meters. 



Air Thermometer. — The construction of the Standard Air Thermo- 

 meter is still delayed, Professors Thorpe and Riicker not having yet com- 

 pleted their comparisons between the mercurial and air thermometers. 



By the kindness of Professor H. A. Rowland, of the Johns Hopkins 

 University, Baltimore, U.S.A., the Committee has had the oppor- 

 tunity afforded it of comparing with a number of Kew standards, 

 one of the thermometers which Professor Rowland has employed 

 in his researches on the deviation of the mercurial from the air 

 thermometer. The instrument is that — Baudin, No. 6166 — which 

 Dr. Joule (" Proc. Amer. Acad. Arts and Sciences, 1880 ") com- 

 pared with the instrument he used in his determination of the 

 mechanical equivalent of heat ("Phil. Trans., 1878 "). Professor 

 Rowland has kindly promised to present the Committee with another 

 of nis standards, which has been compared with his air thermometer 

 throughout a greater range of scale than the present instrument. 



V. Verification of Instruments. 



The following magnetic instruments have been verified, and their 

 constants have been determined : — 



A Unifilar, by Gibson, for Elliott Brothers. 



Pour Dip- circles, by Casella. 



A pair of Dipping-needles for Elliott Brothers. 



Three Dipping-needles for Dr. E. Van Rijckevorsel. 



Two Magnetograph-needles for M. Dechevrens, Zi-Ka-Wei. 



An Azimuth Compass for Barker and Son, 



