.1816.] M. Prevost’s Note, in Reply to Dr. Weils. 71 
In the crustacea malacostraca are always to be observed one pair 
of mandibles, two pair of maxille, and sixteen legs, the three 
foremost of which generally assume the form of maxilla and bear 
palpi at their extremities. In /nsecta are to be observed one. pair 
of mandibles, one pair of maxille distinct; the exterior pair 
‘coalescing so as to form the under lip, which, like the interior 
maxillz, bears palpi. 
Such are the important discoveries of the last year, which has 
done more for the advancement of zoological science than: the 
preceding 13 years. 
Articxe II, ae 
Note by Professor P. Prevost respecting Dew, in consequence of the 
Answer of Dr. Wells inserted in N° XXXVI. of the Annals of 
Philosophy. ; 
Arrer reading Dr. Wells’s answer, and before perusing the 
Jetter to which he refers (Annals of Philosophy, vol. v. p. 251), t 
hasten to thank him for the information which he has given me. 
1. I observe, that in explaining the principal pheaomenon to 
which Mr. Benedict Prevost has reduced the results of his experi- 
ments, I have said positively that 1 did not pretend to have ex- 
plained all the details, and that I thought it sufficient to have 
clearly explained one of the causes of that class of facts (Calorique 
Rayonn. § 207). 
2. Dr. Wells thinks that dew can never be deposited upon the 
side of a glass which is exposed to air colder than itself. 
This does not invalidate my explanation, but is inconsistent with 
the assertion of Mr. Benedict Prevost, who affirms that in order that 
dew be deposited on the outside of glasses, it is not necessary that 
the temperature on the outside should be greater than that on the 
inside (cited Calor. Rayonn. § 193, n. 24, p. 241).- In the disser- 
tation itself, from which Ll have quoted a mere extract, that philo- 
sopher says expressly “ that exterior humidity is very often deposited 
though the external air be colder than the internal.” Mr. Benedict 
Prevost supposes this fact in his first generalization (cited Calorique 
Rayonn. § 194, n. 1). I intend to request him to give us his 
roofs, 
All this discussion must tend to the advantage of the science. I 
am delighted, therefore, that Dr. Wells has produced it. This is 
an additional obligation to all those for which science is indebted to 
him, 
Geneva, 1815. 
