of ; ANNIVERSARY ADDRESS. 
by the metograph to be 64°; only 2 few drops of rain fell, and the ’ 
temperature rose again about 2°. As I watched the cumulus and 
the rain in the W.8.W., the clouds slowly descended and became 
lost in the haze. If we may assume that the air at the Observa 
tory was in a similar condition to that all round, we find that at 
noon, and before the sun was covered, the difference between the — 
dry and the wet bulbs was 5-9°; and on that occasion a fall of 
6}° in the temperature produced a few drops of rain ; but in order — 
to cool this air to the dew-point by elevation, its temperature W ould 
have required reduction by 10-4°; or to be raised up 1,870 feet. 
It is probable, therefore, that the clouds forming over Sydney 
that day were about 1,800 feet high. 
These instances are illustrations from nature of the conditions 
under which the leading scientific meteorologists of the day tell us 
that rain is formed. If, however, it so happened, as in temperat® 
latitudes it might, that there was a cold wind blowing over the 
warm satutated one when this up-current was started, then the 
heated air would rush up into it, and when once the stream Wa — 
started there would be a great downfall of rain—in fact we should 
have a case in which the “unstable equilibrium” of the atmo 
sphere having been upset, the downfall of rain would be dispropo™ — 
_ tionate to the cause which set it in motion ; but this condition, 
viz.,a cold current blowing over a warm moist atmosphere, 8° 
very uncommon one, for the cold air being the heavier seeks 
lower position, and can only take the upper one when moving | 
witb considerable velocity. It would therefore rarely happe™ 
that an up-current, even when once started, would continue for 
sey ee 
Ne ee ee SS bheve 
uplifting force would be necessary at any particular place ut until all 
haspuciresmnanmmimertae saeco age cence it would be an es) 
3 iofuite relation 
_ to the amount ot rain damien: Of course this relation would 
= vary with the humidity of the air, with the relative temperature’ 
of the layers of the atmosphere, and with many other conditions + 
and it would be quite impossible to say definitely how much 
