34 MEMOIR OF DR. DALTON, AND 



place of Dr. William Henry, and having as his colleague Dr. 

 Hull. This office he retained until the year 1608, when he 

 was made vice-president in the room of Dr. Roget, who then 

 lived in Manchester. Soon after, on June 27 th, he read to that 

 Society, *' Experiments and observations on the heat and cold 

 produced by the mechanical condensation and rarefaction of 

 air." * Here by well devised experiments he endeavoured 

 to shew what however had been before held by Lambert, 

 Saussure, and Pictet, " that the capacity of a vacuum for 

 heat is less than an equal volume of atmospheric air, and 

 that the denser air is, the less is its capacity for heat," indi- 

 cating a mode of ascertaining " the absolute capacity of a 

 vacuum for heat," and " likewise the capacity of the different 

 gases for heat by a method wholly new." An important 

 result of these experiments was, that the temperature of air 

 mechanically compressed to one-half its volume was raised 

 50°. This, although much underrated, was the first nume- 

 rical result of importance on this subject, p. 524. 



In this paper we find that he had ascertained that gases 

 expand 1-lOth of their volume nearly for 50° of heat, or 

 nearly 1 -500th of their bulk, a subject which he treated of 

 at a later period. 



Whilst engaged in teaching at the academy in Manchester, 

 his classes or scholars seem to have been as miscellaneous 

 as they had been at Kendal. We may infer this from the 

 appearance of an English grammar, the preface of which 

 is dated March 10th, 1801. He seems to have looked 

 on this as a recreation, but he never afterwards appears 

 to have had recourse to literature for amusement or for 

 variety. As he has never been looked on as a grammarian, 

 it may be of some interest to see what his views on such 

 points were. 



He says, p. 8. " It may be taken as an axiom that all 

 time or duration in the strict sense of the terms, is either 



• Mem., Vol. V., p. 516. 



