THE MEASUREMENT OF TEMPERATURE. 79 



•of ordinary temperatures, for which purpose I consider it 

 well suited. 



With regard to the difficulties of making observations 

 with this instrument, those who urge this point evidently 

 suppose that in order to obtain a temperature by a mercury 

 thermometer it is merely necessary to observe the position 

 •of the top of the mercury column, and if they desire no 

 greater accuracy than is obtainable without further exer- 

 tion I admit that simplicity is on the side of the mercury 

 thermometer. Where accuracy is required I think that I 

 have shown in Section I. that the use of the mercury ther- 

 mometer is by no means simple, and that when we bear in 

 mind the labour involved in the previous processes sim- 

 plicity is all on the side of the platinum thermometer. 



As to the difficulty of constructing the instrument, I am 

 not aware that observers usually manufacture their own 

 mercury thermometers, and since platinum thermometers 

 are now supplied commercially the objection bears but little 

 weight. 



In conclusion, I would again quote from Callendar's paper 

 (9) : " I quite admit that it requires some special skill and 

 experience to make a good thermometer, but the rest of the 

 apparatus required is obtainable in almost any laboratory and 

 it is easy to take the readings quickly and accurately after a 

 little practice. The great superiority of the platinum ther- 

 mometer in range, accuracy and durability will be found in 

 the end to save as much time and expense as will more than 

 compensate for the small trouble of learning to use it.'' 



BIBLIOGRAPHY. 



(1) Report of the Committee on the Siemens Pyrometer. B. A. 



Report, 1874. 



(2) Account of Sir William Siemens's Experiments. Trans, of the 



Society of Telegraph Engineers, 1875. 



(3) CALLENDAR. The Practical Measurement of Temperature. 



Phil. Trans. Roy. Soe., vol. clxxviii., 1887. 



(4) Griffiths. The Graduation of Mercury Thermometers by 



Means of Platinum Thermometers. B. A. Report, 1890. 

 iS) Heycock and Neville. The Melting Points of Alloys. 

 Chem. Soc. fourn., 1890. 



