104 Mr. J. H. Alexander 07i the Tensionof Vapour of Wate)\ 



Sucli are the conclusions that arise from the comparison 

 with M. Regnault's experiments. 



2. Experiments of the Franklin Institute. — The temperatures 

 were read by these observers to only the nearest quarter of a 

 dej^ree of Fahrenheit ; they are therefore not comparable in 

 precision, whatever they may be in accuracy, to those that 

 have just been considered. And as but one reading either of 

 temperature or pressure is given in each instance, they do not 

 allow of being treated in the method that has just now been 

 applied. I can only then compare them as in the following 

 table : — 



The temperatures of the Academy in this table were not, 

 as has been said already, from experiments at the precise 

 epochs of pressure, but were interpolated from experimental 

 terms not remote. Under a general principle, 1 excluded 

 them from the comparative table in the preceding memoir ; 

 but they satisfied even the fastidiousness of M. Dulong, as 

 representing accurately the results of observation, and are 

 therefore fit to be compared as they are here. The last line 

 o{ mecm differences shows the excess of the formula-tempera- 

 tures above those of the Academy to be not much more than 

 one-third of the excess of the latter above those of the Franklin 

 Institute ; the probability of accuracy of these last, then, at 

 most cannot be more than in the same ratio. It also shows a 

 mean error between the formula adopted by these observers 

 and their observations, of 0^'36; by which deviation the 

 former, with the advantage of having the two extremes arbi- 

 trarily to coincide, yet fails to adjust itself to the latter. 



3. Experiments of the French Academy of Sciences. — Out of 

 the whole of this series M. Dulong has himself selected ^/^w» 

 as the most unexceptionable, and has used them for a standard 



