144 Dr. E. J. Mills on Thermometry. 



confusion in the minds of my critics, I am not prepared to 

 suggest a remedy, and must leave their very lengthy disqui- 

 sition upon this point entirely unassailed. I should add here, 

 that I have nowhere alleged that the motion of a thermo- 

 meter's zero has any particular limit. 



The remainder of the remarks of Professors Thorpe and 

 Rucker under this heading comprise a short dissertation 

 (page 9) on the prudence that should be observed in applying 

 mathematical expressions to represent the results of experi- 

 ment. This passage appears perfectly clear, though perhaps 

 not wholly novel ; but I have so far failed to follow the rest of 

 this section, that I am unable to discuss it. Perhaps it will 

 be satisfactory if, mathematical formulae apart, I make a state- 

 ment of matters of fact within my own knowledge. 



When a vacuous mercurial thermometer is heated to suc- 

 cessively higher temperatures, its zero continues to fall until 

 some particular temperature (say 150°) is reached. After this 

 the zero commences to rise (I must not say " ascend "), as the 

 temperature increases to another particular stage (say 340°). 

 Between these two phenomena there must be a "turning- 

 point." As the temperature continues to increase, the zero 

 again falls ; this, of course, involves another " turning-point." 

 The "rising" in the second stage often amounts to as much 

 as 3° or 4° ; this enormous effect I can attribute to no other 

 cause than atmospheric pressure. 



3. The remaining criticisms do not, as I conceive, involve 

 the imparting of information. It will therefore be sufficient 

 for me to reply that to the statements made in my memoir I 

 still strictly adhere. Some experiments of their own, referred 

 to towards the end of their paper, are cited by its authors 

 a propos of a "rising zero," which I have not defined as they 

 suppose. 



Professors Thorpe and Rucker indicate that they may have 

 occasion subsequently to further discuss my " Researches." 

 Should they thus honour me, I trust it will be to really essen- 

 tial and important points that they will direct their attention, 

 and preferably by way of experiment. An obvious misprint, 

 a slip in arithmetic, a question of mere nomenclature, and the 

 like are trivialities unworthy, in my opinion, of grave and 

 lengthy publication. 

 Glasgow, July 1881. 



