r 330 ■] 
•was thus cooled, I breathed on it repeatedly, till its 
polifhed furface was covered over with an inciudation 
of ice or frozen vapour, of a very palpable thicknefs. 
In this condition the fpeculum was replaced in its for- 
mer fituation, having its incrufled furface expofed to 
the ftill open air; when, in a little time, w'e found 
the frozen pellicle begining to difappear at the outer 
•edge, all around, leaving the metal quite clear. 
Gradually more and more of the fpeculum was bared 
in a regular progreflion, from the circumference to- 
wards the centre; and at laff, in about 50 minutes, 
the whole furface had parted with "its ice. This ex- 
periment was repeated when the fpeculum was de- 
fended from the open air, by a large thin box, with 
a cloth over it. The event turned out the fame as 
before, only it required longer time. 
This progrefs of the evaporation from the outward 
parts towards the centre of the fpeculum, was likely 
owing to the original plate of ice being thickeft to- 
wards the center, a ciixrumflance which might arife 
from the manner of fixing it at firff breathing on it. 
Or perhaps it may be imputed to fome more curious 
caule, and may be lome effedt of the repullive force 
belonging to the poliflied furface ; but, this point we 
did not fufficiently examine into, by a due repetition 
of experiments. I may juft mention, that, partly 
with a view to this matter, we expofed as above, a 
fet of bodies, having their furfaces of different de- 
grees of polifli, and as equally covered with frozen 
moifture as we could judge. The refult of which 
experiments feemed to favour the idea of the ice 
being lefs attached to the more polillied furface than 
to the coarfer. This appeared particularly in the 
