436 PROCEEDINGS OF THE SCIENTIFIC ASSOCIATION. 
f 
small descent on the following day — we may generally in- 
fer that the atmosphere over our heads is supercharged 
with the vapour of water. As water, when converted into 
invisible vapour, is very much lighter than air, and inter- 
penetrates and mixes with it,' it is easy to perceive that 
the air thus mingled with watery vapour will be lighter 
than the undiluted air in its normal state, and hence less 
pressure will act on the mercury in our barometer. Under 
these circumstances we might reasonably expect a fall of 
rain shortly. 
But if we perceive a rapid descent of the mercury in 
our barometer— say two-tenths of an inch (or even less 
than that) in an hour, and that it continues to go down — 
then let us lose no time in looking after our defences 
against the approaching foe. Be not beguiled by the ap- 
parent fineness and serenity of the weather at the moment, 
for so sure as such indications as we have just referred to 
shall be disclosed by the barometer, so certain is it that a 
heavy gale is near at hand. Let us first secure .our doors 
and windows that front the east , the north and the west ; — 
for as a hurricane cannot commence from the south , we may 
attend to the southern fronts of our buildings afterwards. 
In offering to the Society this little Essay on “ coming 
tl weather and on weather predictions,’ ’ we have endea- 
voured to show, that neither from experience, nor by any 
legitimate principles of science, have we any grounds to 
justify us in presuming to predict any particular condition 
of weather beyond the continuance of at most a few hours. 
We have also adverted to the erroneous notion that the 
configurations of the sun and moon have any influence 
whatever on atmospheric disturbances. The dreams of 
astrology have passed away. Wo must bring our belief 
