PHYSICAL LABORATORY OF GREAT BRITAIN. 355 



But the results of no two series of observations which have been 

 made agree satisfactorily. The variations arise prol^ably in great 

 measure from the fact that the English glass thermometer as ordina- 

 rily made and used is incapable of the accuracy now demanded for 

 scientific investigation. The temporary depression of the freezing 

 point already alluded to in discussing tho ,Iena glass is too large; it 

 may amount to three to four tenths of a degree when the thermometer 

 is raised 100 . Thus the results of any given comparison depend too 

 much on the immediate past history of the thermometer employed, 

 and it is almost hopeless to construct a table accurate, sa}', to 0.01, 

 which will give the ditierence between the Kew standard and the 

 hj^drogen scale, and so enable the results of former works in which 

 English thermometers were used to be expressed in standard degrees. 



Values of corri'ctioiis to (he EnrjUsh glass-tJiermomeler scale to give Uinpendures on tlie gas- 

 thermometer scale found by various obserrers. 



Tl'Diii. Kowhuid. Guilhuiim;. Wielx- 



o O I 







10 — .03 — .009 + .03 



20 - .05 - .009 + .00 



30 - .06 - .002 + .02 



40 - .07 + .007 + .09 



50 - .07 + .016 + .14 



60 - .06 



70 - .04 



SO - .02 



90 — .01 



100 



This is illustrated by giving the ditl'erences as found (1) ])y Rowland, 

 (2) by Guillaume, (8) l)y A\'iebe, between a Kew thermometer and the 

 air thermometer. It is clearly important to establish in England a 

 mercury scale of temperatures which shall be com})arable with the 

 hydrogen scale, and it is desirable to determine, as ncarl}" as nuw be, 

 the relation between this and the existing Kew scale. 



I am glad to say that in this endeavor we have secured the valual)le 

 cooperation of Mr. Powell, of tiie AViiitefriars works, and that the 

 first specimens of glass he has submitted to us bid fair to compare 

 well with the 16"'. Another branch of thermometry at which there 

 is much to do is the measurement of high temperature. Professor 

 Callendar has explained here the principles of the resistance ther- 

 mometer, due first to Sir W. Siemens. Sir AV. C. Roberts-Austen 

 has shown how the thermopile of Le Chatellier may be used for the 

 measurement of high temperatures. There is a great work left for 

 the man who can introduce these or similar instruments to the manu- 

 factory and the forge, or who can improve them in such a manner as 

 to render their uses more simple and more sure; besides, at tempera- 

 tures nuich over 1,000^ C. the glaze on the porcelain tube of the 



