326 J. He Alezander on the Tension of Vapor of Water. 
rections for reduction, appears ¥ diminish per the chances — 7 
of practical resort to the table itself. se temperatures, Mr i 
Biot, in the form first proposed fe Prony, “GHB same which Dr.  ~ 
Youn ng, with more emphasis than reflection, has called “ ridicu- 
lously complicated,”) employs as the exponents of a series ; the 
peculiarity of the method, however, is in that the direct numeri- = y 
cal result of the equation gives, instead of the pressure itself, i 
tabular logarithm of the pressure. It is, therefore, essentially a 
logarithmic formula. 
I present the following comparison between it and the present 
formula; applied to the same instancés of experiment, which 
have been already signalized by Mr. Dulong himself, and already : 
quoted here. ‘T'o save both the tedium and hazard of a reduction 4 
to English measures, : eve the quantities under their origin 
denominations and, in so far varying from the preceding instan-— . 
ces, I give the oviation of the formule in terms of the pressure 
‘instead of the temperature. ‘This method enables me, by an easy 
and safe interpolation, to extract the proper quantities from Mr., 
Biot’s table ; and thus to avoid the nok ahetls labor of workings 
out the numerical transformation of his theorem. 
No. of |. Temperatuies, RCenughade} Pressures in Metres; 
>| Experi- Mercuria Air By Biot’s Observed by By present , 
, _|_ment. | thermometer. | thermometer. formula. Dulong & Arago. ate 
wee bee Bs 123°-7 239-1: 1-65020 1-6291 162022 | 
. 133 3 132-47 2:26396 2:1816 687 — 
149 -7 148 -41 3°47146 3:4759 3:37449. 
163 °4 161 -69 4:94220 4:9383 + 4-80439 —~ 
168-5 ° 166 -63 560263 5 6054 545121 7 he 
188 +5 185-96 8.89046 840 8 
206 -8 203 -60 13:05578 13-061 13:04525 
207 °4 204 +18 13-21410 13-137 13-21 202 
210 -5 207 -16 05179 14.0634 
218 -4 214 +75 16°36717 16-3316 1660100 | 
224-15 2 1804 18-1894 18:64254 | 
ON embarrass this table with so many columns, I omit the 
‘individual deviations of the two formule ; and present the aay 
gal result as under. ; 
4 Mean devi ti fi t e | Alesode 
ation from experimen 
ew pent regard to signs m ‘ O52066 0-:12191 
an 
= o pans, from experiment be - 0-0170 4» 0-02114 
It is hardly necessary to repeat that the first of these formule is. 
founded in part upon the very prperiments with which it accords” 
so well; and that the other was 
The table of Mr, Biot goes up as far as 220° Cent. ; but he 
supposes that his formula is applicable much father ; and i in fact 
_he has given results; in a small supplementary table, as high as” 
300°C ; at which temperature it makes the pressure 
ual to almost exactly 85 atmospheres. ‘The present formula 
