88 MR. T. HOPKINS ON IMPROVEMENT 
In order to obtain this knowledge it is necessary that 
the metamorphoses of water should be traced, as has been 
here attempted in the case of Toronto. We have seen, in 
that place, that evaporation of water increases atmospheric 
pressure up to nine o’clock in the morning. But after 
this hour the vapour parts with its heat of elasticity, 
which heat then adds to the elasticity of the gases, and 
lightens them, and we wish to know to what extent this 
is done. The energy, or rate, of evaporation is the best 
evidence that we have of the quantity of vapour that is 
sent into the atmosphere, and therefore this energy should 
as far as possible be shown. In July at Toronto it was at 
2°01 at four o’clock in the morning. At nine it was at 
5°81, and at five in the afternoon it was at 9°45. Yet 
after nine in the morning the quantity of vapour found in 
the air as shown by its tension became less, and it follows 
that all the vapour which ascended after nine o'clock, toge- 
ther with the portion that was no longer found in the tension, 
disappeared ; and there is no doubt that it must have been 
condensed into liquid in the higher regions. And as we 
presume that this condensation liberated the heat which 
caused the fall of the barometer at Toronto, we might 
infer the extent to which that instrument would sink in 
other parts, if we could ascertain how much vapour is sent 
into the atmosphere and condeused under similar circum- 
stances in those parts. Or we may proceed in the reverse 
course, and from the fall of the barometer infer the 
amount of vapour that had been condensed in the upper 
regions. 
The aqueous portion exercises so important an influence 
on the movements of the whole mass of the atmosphere as 
to require that its metamorphoses should be traced with as 
much accuracy as possible, and particularly that portion of 
vapour which ascends from the time that the barometer 
begins to fall in the morning, until that instrument turns 
