IN METEOROLOGICAL REGISTRATION. 83 
instead of then becoming less, it became more energetic, 
and increased until five o’clock in the afternoon, when it 
was at 9°45, making an increase in the energy of evapo- 
ration from nine in the morning until five in the afternoon 
of 3°64, yet, notwithstanding this increase of evapora- 
tion, the barometer fell no less than 0°0496. It is, however, 
to be noticed, as may be seen from the table, that though 
evaporation had so greatly increased, the tension of yapour 
was somewhat reduced after nine o’clock; yet that reduction 
was small compared with the fall of the barometer. The 
tension was found at nine o’clock to be 0°5550, from which it 
became reduced until at five it was only 0°5190, but the ba- 
rometer fell during the same time from 29°6084 to 29°5588. 
Thus it required an increase of 0°1130 of vapour tension in 
the morning to raise the barometer 0°0253; but a fall of that 
instrument afterwards until five in the afternoon of 0:0569 
was accompanied by a reduction of only 0:0360 of tension. 
So that tension of vapour is exhibited as being powerful 
compared with temperature, the other varying constituent 
of pressure, in the morning, and feeble in the evening, 
involving a mass of contradiction and confusion. 
From these statements, however, it beccmes sufficiently 
apparent that the weights of the constituents of atmo- 
spheric pressure cannot be inferred from the tension of 
vapour, seeing that the vapour which passes into the 
atmosphere between nine and five does not appear in the 
tension. I have shown elsewhere how the vapour that 
passes into the air at this time of the day reduces, instead 
of increasing, tension, but the aqueous matter in the 
atmosphere must evidently be increased by the evapora- 
tion; though there are no means of measuring the extent 
of that increase, unless we ascertain directly the quantities 
of water evaporated. Yet whatever the quantity may be, 
when it does not fall as rain, it remains in the air either as 
vapour or as cloud. And while in the air as cloud, it does 
