528 Dr. M. W. Travers and Mr. A. G. C. Gwyer. [Jan. 11, 



Professor Judd has enabled me to try the action of radium emana- 

 tions on specimens of this glass. Fifteen milligrammes of pure radium 

 bromide sealed in a quartz tube were put close to a sample of the 

 deepest green glass. In two days appreciable darkening took place, 

 and in 10 days the darkening was very marked. 



A similar experiment was tried on a sample of the purple-tinted 

 glass ; here also the action was the same as in the former case, and in 

 10 days the darkening was about the same. Allowing for the apparent 

 alteration of colour caused by the initial tint of the two pieces of glass, 

 I should say the colour produced by radium was similar in each case, 

 and was of the same purple colour as that caused by long exposure to 

 sunlight.] 



" On the Comparison of the Platinum Scale of Temperature 

 with the Normal Scale at Temperatures between 444 and 

 190 C., with Notes on Constant Temperatures below the 

 Melting-point of Ice." By MORRIS W. TRAVERS, D.Sc., 

 F.R.S., and A. G. C. GWYER, B.Sc. Eeceived January 11, 

 Read January 26, 1905. 



Introduction. During the last few years one of us has been engaged 

 in researches involving the accurate measurement of low temperatures. 

 The measurements were made by means of gas thermometers, of the 

 constant volume type, filled with hydrogen, or with helium, at an 

 initial pressure of 1000 mm. As, however, this method proved 

 cumbrous and inconvenient, it was decided to standardise a platinum 

 resistance thermometer of the Callendar type against the gas ther- 

 mometer, and to employ it in future investigations. The comparison of 

 the thermometers between - 190 and 444 C. has been carried out 

 with considerable accuracy, and as the range of temperature overlaps 

 that investigated by Callendar and Griffiths, and by Harker and 

 Chappuis, we have decided to publish our results, though from our 

 own standpoint the work is only considered as preliminary to other 

 investigations. 



In expressing our results we have employed Calendar's notation. 

 Thus, when R is the resistance of a coil of platinum wire at the 

 melting point of ice, and RIOO is its resistance at the temperature of 

 saturated steam under absolute standard pressure, which in the 

 laboratory of University College, Bristol, is equivalent to 759 '55 mm. 

 of mercury at zero, the value of the coefficient of change of resistance, 

 a, is given by 



RIOO RQ _ 

 lOORo 



