222 J. H. Alexander on the Tension of Vapor of Water. 
of the press; since it makes its appearance in both ways of reck- 
oning, by atmospheres and by metres 
‘I do not know how to account for another discrepant pressure, 
corre nding to the temperature 405°*04; which has been indi- 
cated by a note of interrogation. On both sides, above and be- 
low, the observed pressures are higher than the calculated one ; 
in this instance, it is suddenly lower. It agrees, to be sure, with 
an independent calculation by the formula of Dulong and Arago, 
at the temperature ; but very manifestly breaks the uniformity or 
any regular progression of the series. What adds to the difliculty, 
is that the same observation is given again in another part of the 
Memoir of the Academicians; but the ciphers do not agree. I 
have neither altered nor omitted either of these instances ; it is 
obvious that they” are not to be used in comparison with the 
present formula. ~ 
The temperatures - the Franklin Institute, which were taken 
for the composition of the table, come from the second series 0 
their reported experiments. Pressures have been also taken from 
both the other series, when their temperatures were already in 
the table ; and, adopting this method as a uniform system, I did 
not allow myself to exclude the anomaly which shews itself be- 
tween the different series at the temperature of 300°. 
Of the experiments of Mr. Regnault, I have already spoken 
sufficiently. 
It is apparent; upon a slight examination of the table, that the 
calculated pressures do not differ more from the average of the 
experimental ‘onés, than these experimental ones do among them- 
_ selves; which is ‘about as much as could be desired to shew the 
ae _walidity of the formula, and the reasonableness of its application, 
‘The mean n of ‘the in diderenotad is +1°-09 Pelee 
heit ; which is the maximum error of the formula, compared wi with 
‘six series. | ae . wel a 4 eS a ee ~ 
