144 MR. J. P, JOULE ON DALTON’S DETERMINATION 
imputed to him, at once occurred to me. I therefore, on 
consulting Dalton’s works, was not surprised to find that 
his commentators had entirely misunderstood the facts of 
the case. These are as follow: — Dalton, in his Experi- 
mental Essays, read before this Society in the month of 
October 1801, describes experiments on the expansion of 
air by heat, the results of which, referred to the freezing 
point, are accurately stated by Regnault. But in the New 
System of Chemical Philosophy published in 1808, under 
the article Temperature, Dalton, while explaining his New 
Table of Temperature, writes —“The volume at 32° is 
taken 1,000, and at 212°, 1,376 according to Gay Lussac’s 
and my own experiments. As for the expansion at inter- 
mediate degrees, General Roi makes the temperature at 
mid-way of total expansion, 1164° old scale; from the 
results of my former experiments (Manch. Mem., vol. 
v. part ii, p. 599) the temperature may be estimated at 
1194°; but I had not then an opportunity of having air at 
32°. By more recent experiments I am convinced that 
dry air of 82° will expand the same quantity from that to 
117° or 118° of common scale, as from the last term to 
212°.” The first part of the above extract contains the 
passage quoted by Regnault, but its meaning is obviously 
not that which he infers. The experiments which Dalton 
states to agree with Gay Lussac’s are clearly some unpub- 
lished ones made subsequently to those described in the 
Manchester Memoirs. Ue nowhere that I can discover 
advances the assertion, attributed to him by Gilbert and 
adopted by Rudberg and Regnault, that his former “ ex- 
periments” agree exactly with those of Gay Lussac. They 
were, however, highly important at the time when they 
were made, and justified the approximately correct conclu- 
sion he drew, that all elastic fluids under the same pressure 
expand equally by heat. 
Dalton was at once aware of the immense importance of 
