that connects the Volume of a Liquid with its Temperature. 405 
zero of gaseous tension [ —461° F.,or —273°-89C.]; then we have 
T,—Ty 
| Fe — SENT 
2@)-G 
and since p= : , we obtain the index of the power of the density 
of the liquid, which being set off as ordinates to the temperature, 
ought to range in a straight line; and this line produced, cuts 
the axis of temperature at y. If, when these points are con- 
nected by distinct lines, a general convexity in the range can 
be discovered, viewing it foreshortened with the eye close to the 
plane of projection, then we may infer that p requires to de di- 
minished if the convexity 1 is directed upwards from the axis of 
temperature, and vice versd. 
§ 9. Having found p and k and y, the next step is to compute 
the values of ¢ from the volumes by the equation, and tabulate 
the differences between the computed and observed temperatures. 
This will be found attended with but little additional labour. If 
we now project these differences as ordinates on an exaggerated 
scale to the temperatures, we obtain a distinct impression of how 
far theory and observation accord. 
§ 10. Mercury and alcohol being the most important liquids 
for thermometric purposes, may serve as examples of the mode 
of computation. 
I. Mercury. 
M. Avogadro’s observations on the tension of the vapour of 
mercury :—At 260° C. the observed tension was 13362 millims., 
at 290° it was 252°51 millims. The correction to reduce the 
temperatures to the air-thermometer from the scale is 5°:60 at 
260°, and 6°91 at 290°. Hence— 
260— 5°60 + 273'89=528:29=T,, 133-62 millims. =e, 
290—6'91 +273'89=556'98=T,, 252°51 millims. =e, ; 
and we arrive by computation at log h=2°54796 and g=247°-45, 
[I have computed the temperatures for M. Avogadro’s other 
six observations. The computed, minus the observed, is, at 
300= + 0°15 
290= -0 
280= + 0°42 
270= —0°26 
260= 0O 
250= —0°26 
240= — 1:90 
230 = —4'56 
= difference in tension amounting to one-third inch mercury. ] 
