122 John Adie, Esq., on the Cause of Change 



Experimental Investigations to Discover the Cause of the Change 

 which takes place in the Standard Points of Thermometers, 

 By John Adie, F.E,.S.E., F.R.S.S.A. Communicated by 

 the Author. 



It has long been known to experimentalists that, in ther- 

 mometers constructed with the greatest care, a change takes 

 place after a lapse of time in the standard points, as given 

 by the melting of ice and boiling of water under a fixed pres- 

 sure ; on this account it has been recommended by most 

 writers, where the employment of thermometers is treated 

 of, that they should from time to time be compared one with 

 another, and also at the freezing point. This change is a 

 rising of the mercury in the tube, so that, after a length of 

 time, the mercury will not sink to the point laid off in the 

 construction of the instrument. To investigate to what 

 cause this change was due, formed the object of my experi- 

 ments : Was it a change in the glass of which the bulbs 

 are formed, or in the mercury with which they are filled ? I 

 was aware that thermometers filled with alcohol were not 

 subject to this change, which would lead to the inference, 

 that the change was in the mercury and not the glass ; but 

 then, in the spirit-thermometer, air is left above the column 

 of spirit, whereas, in those constructed with mercury, the 

 air is expelled, and there is a vacuum above the column ; 

 consequently, the bulb is pressed together with the force of 

 an atmosphere on all sides ; might not this force, acting for 

 a length of time, cause some small alteration in the arrange- 

 ment of the particles forming the glass of the bulb % 



This is the explanation accepted by most of the Italian 

 and French writers on this subject. Some suppose that the 

 mercury may contain air and moisture within its particles ; 

 but such a hypothesis I think inadmissible, as in the case of a 

 vacuum over the mercury, these particles would seek the void, 

 and cause rather a depression than a rising of the freezing 

 point. Mr Daniell, in his Essay on Climate, adopts the same 

 view ; and Sir John Herschel, in his article " Heat," in the 

 Encyclopaedia Metropolitana, says : " The freezing point upon 

 the mercurial thermometer has been supposed to undergo 



