214 J. H. Alexander on the Tension of Vapor of Water. 
thirty times larger, both the attainment of equal precision requires, 
and the facility of calculation allows, another decimal place to 
be taken. 
These decimal constants might, indeed, have been given in both 
formule at once, instead of the fractional expression from whic 
they originate ; were it not that I thought it desirable to preserve 
those factors which, besides solving the equation, indicate also, 
in part accidentally and in part essentially, certain elementary re- 
lations between pressure and temperature, (or rather certain epochs 
in those relations,) which are important in the future complete 
theory of the subject. For example, the denominator (1695) 
which expresses the number of volumes of steam under the at- 
mospheric pressure and at a temperature of 212°, developed from 
an unitary volume of water at its maximum density,—shows also 
the number of atmospheres, the equivalent of whose pressure 
will, below a certain temperature, prohibit the developement of 
steam beyond the sphere of said unitary volume. On the other 
hand, the numerator (990°) gives this limiting temperature ; and 
shows the degree on Fahrenheit’s scale, where the force of steam 
becomes equivalent to 1695 atmospheres. Its density, therefore, 
would be equal to that of water; if its behavior in other regards 
were like that of water too, this temperature would be the limit 
to its useful effect. But as there would most probably still re- 
main the elasticity due to its expansidn at that temperature, it 
aon not appear that we are Warranted in supposing any such 
imit 
At this point, 990°, the ratio of the latent and sensible heats, 
expansion due to the temperature, is (with Gay Lussac’s factor) 
0-975 of the unitary volume; the expansion of water, due to 
the same temperature (taking its maximum density as occurring 
at 39°-4 F"., its actual expansion as 0-04333 at 212°-F., and its 
rational expansion as the cube-root of the fifth power of the 
