166 Report of the Kew Observatory Committee. 



suggested by the experience of Dr. Harker and the Observatory staff. 

 On its completion, this box was taken to Sevres by Dr. Harker in 

 July, together with two or three of the platinum thermometers pre- 

 viously in use at the Observatory, and some new ones of higher 

 resistance. Since then Dr. Harker has been engaged on the proposed 

 research in co-operation with Dr. Chappuis of the International 

 Bureau. It is expected that the investigation, so far as practicable 

 at present, will be concluded in a few months. 



The inconsistencies in the behaviour of the Callendar-Griffiths 

 resistance box, referred to last year, having been proved to arise prin- 

 cipally from the uncertainties of the plugs, it was sent to the makers 

 (the Cambridge Scientific Instrument Company) for readjustment. 

 They made use of the opportunity to introduce, at their own expense, 

 a new system of plugs. In it the plugs are isolated, so that manipu- 

 lating one leaves the tightness of the others unaffected. Another 

 source of trouble proved to be thermo-electric currents generated 

 in the patent thermo-electric key; the key accordingly has been 

 enclosed, at the suggestion of Mr. W. N". Shaw, in a box, and the 

 defect though still existent appears much reduced . 



Experiments have been continued on the fixity of zero of platinum 

 thermometers and the degree of consistency in the results obtained 

 with them. Further attention has also been given to the comparison 

 of platinum and mercury thermometers at high temperatures. This 

 is a subject of increasing urgency in view of repeated requests for 

 direct high temperature verifications which cannot as yet be satis- 

 factorily dealt with. 



Mercury Thermometry. To assist in perfecting a method of high 

 temperature verifications, some high range thermometers of the Jena 

 glasses 16 m and 59 m have been ordered from Berlin. They are to 

 be verified at the Reichsanstalt before delivery. 



At the request of Messrs. Powell & Sons, Whitefriars, experiments 

 are being made as to the therniometric properties of different kinds 

 of glass. Particulars of the chemical composition of the glass 

 will be published, with the results obtained, when the experiments are 

 completed. 



An apparatus for the comparison of meteorological maximum and 

 minimum thermometers in the horizontal position has been designed 

 by Mr. Casella, and is at present under construction. 



Y. VERIFICATION OF INSTRUMENTS. 



The subjoined is a list of the instruments examined in the year 

 1897, with the corresponding results for 1896 : 



