Report of the Kew Committee. 



409 



of the Section d'Horlogerie de la Societe des Arts a Geneve, asking 

 for full particulars of the system of rating at this Observatory. 

 These were forwarded to him, and in acknowledging receipt of the 

 same he expressed the gratification of his Council at the degree of 

 accuracy obtained in the Kew trials during the year. 



Rating of Chronometers. — Application having been made to the 

 Committee to extend their system of watch rating to marine chrono- 

 meters, arrangements were carried out for effecting this. A chrono- 

 meter oven formerly constructed for the Testing Office of the Board 

 of Trade, being unemployed, was obtained on loan from the Meteoro- 

 logical Council, in whose possession it was, and erected with the 

 necessary gas-fittings in the Thermograph-room of the Observatory. 



A scheme for rating and certifying was drawn up, of which the 

 following is a brief abstract. 



The trial occupies 35 days, divided into 5 periods of 6 days each, 

 and 5 intermediate days, namely, 1 day at the commencement of each 

 period of test : — 



1st period. Chronometer at temperature of 55° F. or 13° C. 



2nd „ „ „ 70° „ 21° „ 



3rd „ „ „ 85° „ 29° „ 



4th „ „ „ 70° „ 21° „ 



5th „ ,, „ 55° „ 13° ,, 



Certificates are granted to chronometers which have undergone 

 35 days' test as specified above, and whose performance is such 

 that : — 



1. The mean of the differences in each stage of the examination, 

 between (a) the average daily rate during that period, and (b) the 

 several daily rates, does not exceed one second in any one of the 

 stages. 



2. The mean daily rate has not been affected by change of tem- 

 perature more than one-sixth of a second per 1° F., which is about 

 a quarter of a second per 1° C. 



3. The mean daily rate has not exceeded five seconds in any stage 

 of the test. 



The trials were commenced in August, and up to present date 

 seventeen ordinary marine and one sidereal chronometer have been 

 rated. 



The Astronomer Royal having on enquiry certified as to the 

 excellent working of Kullberg's temperature regulator in the chrono- 

 meter oven at the Royal Observatory, Greenwich, the inventor has 

 ' been instructed to fit a similar one to the Kew testing case. 



A Richard Thermograph has also been procured, and is arranged 

 to work in the case with the chronometers, so as to afford a continuous 



