Dr. Mills's Researches on Thermometry, 7 



of Henrici's thermometer,, the zeros were depressed, and that 

 the depression increased with the temperature to which the 

 thermometer was subjected. 



Immediately after giving the table, however, Dr. Mills says 

 (p. 579): — " The starting-point of the observations with ther- 

 mometer 455 was 168°*6. When in its equation y = 0, 

 #= 10*61, the ascent under the influence of heat was thus 

 converted into a depression after 306°*5." We shall have 

 presently to refer to this change of direction of the motion of 

 the zero. It is for the moment sufficient to say that no expe- 

 riments were made at a temperature so high as 306°, and that 

 therefore over the whole range of the observations the zero 

 ascended. It is, however, hardly fair to the reader to leave 

 him to gather, from the remark just quoted, a fact of which 

 neither the formula nor the table gave any hint, viz. that 

 thermometer 455 behaved differently from Henrici's, and that 

 the zero ascended under the influence of heat. As to what 

 the nature of this ascent was we are in the dark. Does Prof. 

 Mills mean that the first heating depressed the zero, and that 

 by subsequent heatings this depression was diminished ? Or 

 does he mean that the first heating raised the zero, and that 

 subsequent heatings increased this elevation ? We presume 

 the former hypothesis is the correct one; but, as far as we can 

 see, there is nothing either in the formulae, the table, or the 

 text to assure us of this. The fact, however, that in some 

 cases heating raised the zero, probably supplies the reason 

 for retaining the name " total remaining ascent," a descent 

 being considered a negative ascent. But even if this could 

 be justified by the analogy of such expressions as negative 

 acceleration, it certainly does not assist the reader to assume 

 that he will understand that an ascent is really a going down, 

 without informing him of the convention which has been made. 



We have dwelt at length on these poinis, not from any wish 

 to draw attention to mere faults of exposition, but because we 

 have now a much more serious matter to refer to ; and we 

 wish to show that if in this we have misunderstood Dr. Mills, 

 it is because he is not very easy to understand. On page 578 

 Dr. Mills says : — 



" The depresssion at 100° in Henrici's instrument is by far 

 the largest at present recorded. It can easily be shown from 

 the equation, that y = when #=9*35; so that the zero in this 

 case would have begun to rise after the immersion of the bulb 

 in a bath at 143°*5." 



Remembering that 



y=2*100(*981)*-*099(l*360)*, 



