Investigations on Platinum Thermometry at Kew Observatory. 3 



" Investigations on Platinum Thermometry at Kew Observatory." 

 By C. CHREE, Sc.D., LL.D., F.R.S., Superintendent. Com- 

 municated by the KEW OBSERVATORY COMMITTEE. Received 

 December 5, Read December 14, 1899. 



CONTENTS. 



Sect. PAGE 



1. Preliminary. 3 



2, 3. Thermometers 4 



4, 5. Resistance box and coils 5 



6. Nature of the observations 7 



7, 8. Sources of change or error 8 



9, 10. Changes in the " leads " or in the " proportional arms " 10 



11, 12,13. Coil changes 13 



14. Faulty action of the contact piece 16 



15. Shift of the bridge centre 16 



16. Thermo-electric currents 17 



17-21 . Heating due to the battery current 18 



22, 23. Error in the temperature coefficient of the coils, &c 23 



24-26. Error in the box thermometer, & c 26 



27-29. Insufficient immersion 28 



30, 31. Slowness of platinum thermometers 33 



32, 33. Purity of ice, accuracy of barometer, &c 35 



34-39. Uncertainties connected with the determination of the " sulphur " 



point 3*> 



40-45. Constancy of platinum thermometers 42 



46-49. Differences between the thermometers 4V> 



50-52. Accuracy of the observations 53 



53. Improvements suggested in apparatus 56 



54. Further experiments wanted 57 



55. Acknowledgment of assistance 57 



Preliminary. 



1. In 1895 the Kew Observatory Committee decided, in the words of 

 their annual Report, " to instal platinum thermometers at Kew, and to 

 institute an independent series of experiments into their behaviour." 

 The Report adds, "Attention will, in the first instance, be directed 

 more especially to the question of the fixity of the zero and of the funda- 

 mental interval." 



In pursuance of this policy the Committee built a special room, 

 furnished with a fume closet, and purchased from the Cambridge 

 Scientific Instrument Company six platinum thermometers and a 

 Callendar-Griffiths resistance bridge, which was regarded at the time 

 as embodying all the latest improvements. 



In the choice of apparatus arid the construction of the room, the 

 Committee hud the advantage of the advice of Mr. E. H. Griffiths ; 

 while Mr. C. T. Heycock, and Mr. F. H. Neville, as well as Mr. Griffiths, 



B 2 



