ELASTIC FORCES OF AQUEOUS VAPOUR. 591 
attributable, at least in part, to the inequality of range in the 
instruments. I have admitted therefore, that the correction made 
for the portion of the columns not immersed, upon the principle 
which has been explained, may be considered sufficiently exact 
for temperatures up to 145°. 
I have collected in the following tables the results which were 
obtained. The temperatures indicated by the thermometers 
immersed in the liquid are given apart from those indicated by 
the thermometers immersed in the vapour. It will be seen, that 
when water boils at low pressures, the thermometer immersed in 
the water takes a temperature considerably above that one which 
is immersed in the vapour: the difference amounts to 0°°7 at 
very weak pressures ; it diminishes in proportion as the tempe- 
rature of the boiling liquid rises, that is to say, in proportion as 
ebullition is effected at a higher pressure, and it ceases altoge- 
ther when that occurs at the pressure of the atmosphere. Nor 
in the more elevated pressures is a more perceptible difference 
observable: this it was that induced me to inscribe in Table 
V., which relates to these pressures, the mean of the four ther- 
mometers. 
I purposely began this series of experiments at very feeble 
pressures, to enable me to compare the results which it gave 
with those which were obtained for the same temperatures by 
the methods described in the preceding chapters. I have dis- 
covered as perfect a correspondence as could have been desired ; 
it is evident at the same time that for low temperatures the first 
methods are preferable. 
TaBLe IV. 
Series N. 
Thermometers Thermometers Moone 
in the liquid. Mean. in the vapour. Mean. ¥ Difference. 
A. No. 8. No. 7. Observed. | Calculated. 
° ° ° ° ° mm mm 
43°55 | 43°55 |] 42°90 | 42°82 | 42°86 || 64713 | 637896] +or25 
43°55 | 43°59 l} 42°89 | 42°83 | 42°86 || 64°13 . -- 
43°46 | 43°55 l} 42°91 | 42°83 | 42°87 || 6412 
49°50 | 49°495|} 48°95 | 48°99 | 48°97 87°59 
49°52 | 49°50 48°98 | 49°02 | 49°00 87°57 ar Ss 
49°54 | 49°535|] 48°98 | 49°00 | 48°99 87°55 | 877455] --ot10 
54°01 | 54°03 |] 53°44 | 53°51 | 53°48 || 109°52 .. . 
54°03 | 54°035|] 53°45 | 53°51 | 53°48 || 09°60 
54°04 | 54°05 |} 53°46 | 53°52 | 53°49 || 109°64 
