Platinum Thcrmonutry at Kew Observatory. 5 



March, 1896 ; the second tube was found to be broken in August, 

 1896, after a silver point experiment. After repair the thermometer 

 behaved badly, and had to be sent to Cambridge. A third tube 

 cracked in molten silver in December, 1896. The fourth tube lasted 

 until the end of 1898, when it was broken at Sevres. On more than 

 one occasion the thermometer had practically to be remade, so that 

 the observations taken with Ko at different stages of its existence are 

 not comparable. The spiral at present in K? is believed, however, to 

 be of the same sample of platinum as the original one. 



The other five thermometers are not known to have had any mis- 

 adventures. 



The thermometers K 2 and K 5 were taken by Dr. Harker to Sevres 

 in July, 1897, and did not return to Kew until the end of 1898. No 

 use was made of K 5 at Sevres, but some observations were made with 

 Ko up to a temperature of about 600 C. 



3. In an ordinary platinum thermometer, it is possible for the air 

 inside the tube to become unduly moist, with consequent deterioration 

 of the insulation. In a glass tube the presence of moisture may be 

 detected by the cloudy appearance when the thermometer is cooled in 

 ice ; in the case of a porcelain tube the only guide is the behaviour of 

 the galvanometer. If there is- no sensible creep in the galvanometer, 

 it is probably best to leave the thermometer alone, even if slight 

 cloudiness is visible. There is some risk of altering the apparent zero 

 of the thermometer in removing it from the tube, and replacing it 

 after the tube has been dried out. On the rare occasions when a tube 

 has been dried out, check observations have been taken before and 

 after the process. The room in which the platinum thermometers are 

 kept is heated night and day when necessary by a gas stove, whose 

 combustion products escape by a flue opening outside. As the room 

 is naturally a dry one, the risk of moisture has thus been small. 



Resistance Box. 



4. The box as it originally existed in 1895 had a plug system 

 similar to that of the ordinary Post Office pattern. The plug holders 

 were of brass. Towards the end of 1896 it was found that pulling 

 out a plug influenced the tightness of its neighbours. .Early in 1897 

 the Committee arranged with the authorities of the International 

 Bureau of Weights and Measures that Dr. J. A. Harker should 

 proceed to Sevres, and take part in a comparison of platinum and gas 

 thermometers. At first it was proposed to take the existing Kew box 

 to Sevres ; but, on hearing of the difficulties experienced with it, the 

 Committee decided that Dr. Harker should examine into their reality 

 before a decision was come to. Finding that with an ordinary 

 standard of plug tightness sufficiently consistent results were not 



