118 
JOURNAL OF THE PLYMOUTH INSTITUTION. 
the weight increases more rapidly than the resistance, and ultimately 
precipitation follows : — thus, if eight spherical particles unite, they 
form a spherical drop whose weight is increased eight times, whilst 
its surface, on which alone the resistance depends, is increased four 
times only; hence the resistance in relation to the weight is only 
one-half of what it was; if twenty- seven particles coalesce the 
relative resistance is diminished to one third; and so on, the 
relative resistance being inversely as the cube root of the weight. 
Clouds, however, may, as such, retain their places and heights 
unchanged for lengthened periods, whilst the matter composing 
them is ceaselessly descending: thus, every one has frequently 
seen a cloud apparently stationary on a mountain top, and sharply 
cut off at some distance below it. An approach to it, however, 
dispels this appearance, and at once shows, except in perfectly calm 
weather, that the cloud-matter is constantly descending on the 
leeward side of the hill, where, on reaching a well-defined line, it 
is re-melted into invisible vapour, to have its place supplied by 
matter constantly arriving from the windward side, where the 
reverse, or condensing process, is in full operation. 
It is obvious that the rainfall and number of wet days on high 
ground will exceed those at lower levels; that winds from the 
ocean and from warm directions will be wetter than from conti- 
nental and cold quarters ; that in Western Europe, the wet winds 
are those from the south and west ; and that lands on that side of 
lofty eminences will be wetter than those on the opposite side. As 
a matter of fact, it is found that if lines be drawn from the 
northern and southern points of Dartmoor in a north-east direction, 
all places in Devonshire between those lines and on the east of 
Dartmoor will be drier than those places in the county which are 
not thus situated. 
It is obvious too that in wet weather, when the whole atmo- 
sphere is supersaturated from the upper cloud region to the ground, 
gauges ahove the ground will receive less rain than those that are 
on it, since the latter receive all the rain that falls, but the latter 
only a part of it ; and thus the defect will be an inverse function 
of the height of the gauge. Some of the rainfall returns published 
annually by Mr. Symons are not only useless but absolutely mis- 
chievous, from being obtained from gauges placed, as at Plymouth 
and some other places, at great heights above the ground, and in 
crowded streets — stations unsuitable on several accounts. 
