THE DEPOSITION OF DEW. 
193 
menttothe tree is by an articulation, like those of leaves, 
fig. A. By this provision sprays are readily detached, 
and the tree relieved from its superfluous branches, 
enabling it the better to resist the winter blasts, 
while, during the summer, they were of service to 
the parent, by furnishing it with the organs of respira¬ 
tion. Did not this annual pruning take place, I am 
of opinion that the tree could not, for so many years, 
have stood, as it is sixty feet high, and its south-west 
side being close to a brook. I know of no other tree 
that detaches living branches, and I consider it a 
curious fact in vegetable physiology.—I remain, &c. 
METEOROLOGY. 
ON THE DEPOSITION OF DEW. 
TO THE EDITOR OF THE HORTICULTURAL REGISTER. 
Sir, —I shall now proceed to detail an experiment I have made, 
since I sent you my last paper, on the subject of the deposition of 
dew, and which, I am happy to say, affords convincing proof of 
the truth of the theory of Dr. Wells. But before I proceed, permit 
me to offer a few remarks on the erroneous views which appear 
to me to have led G. J. T. astray in the formation of his theory. 
I think the chief error into which he has fallen, in this as well as 
in other instances, is in attempting to account for phenomena which, 
in the present state of science, we must be content to consider as 
ultimate facts, or the analysis of which cannot be expected to be 
accomplished without a much more accurate acquaintance with the 
laws relating to them than G. J. T. seems to possess. Another source 
of error arises from the manner in which he has confounded the powers 
of radiation and conduction in the propagation of heat, having in some 
instances spoken of them as the same, though they are two distinct 
processes, each following laws peculiar to itself. I shall not now enter 
into a statement of these laws, as I propose at some future period to 
make them the subject of a separate article, but proceed to illustrate 
by experiment, the way in which these laws are applicable to Dr. Wells' 
theory of the deposition of dew. I procured two boxes about fourteen 
inches square, and without lids; one of tin, the other of wood, coated 
VOL. IV.—NO. XLVII. S 
Bottom of a spray 
to show the articu¬ 
lation. 
