of Dew on Metallic Surfaces. 3 
pose of receiving dew, it was remarked, that the first formation of 
moisture took place at the corners of the triangular portions of the 
metallic paper, not in contact with the wood; the particles beng 
exceedingly minute, and requiring the aid of a magnifying glass to 
discover them. As the radiation of the metallic surfaces was pro- 
moted by the influence of the clear nocturnal sky, those particles of 
moisture gradually increased both in number and size ; while other 
minute drops began at the same time to be deposited on the edges 
of the square; so that in the course of three hours, the metallic sur- 
face had assumed the appearance represented in fig. 1, Plate I. the 
shaded parts denoting the particles of dew, and the dotted lines 
the position of the cross to which the metallic paper was attached. 
After midnight, the farther deposition of moisture appears to have 
been suspended; as at half an hour before sunrise, the appearance 
of the metal was nearly the same as when the last observation was 
made. 
~ It was most interesting to observe, during the progressive depo- 
Sition of the moisture, that the particles were disposed in triangular 
forms, similar to the right-angled triangles, into which the metallic 
paper was divided, by its contact with the cross ; and this was the 
case even when the triangles, from their minuteness, might be es- 
teemed of an almost elementary kind. And at the last observation, 
when the greatest quantity of dew for the night had been depo- 
sited, the triangular figures were perfectly well defined, their hypo- 
thenuses being bounded by the edges of the metallic surface, and 
their several bases and perpendiculars, respectively parallel to the 
arms of the cross. . So also the gradual accumulation of moisture 
in the small segments, whose chords coincided with the edges of 
the metal, was marked by the same uniform and progressive cha 
racter; the particles, during their increase in number and magni- 
tude, preserving a beautiful curvilineal contour to the figures which 
they formed. The parts of the paper in contact with the cross, had 
no dewy particles on them ; their junction with the wood appearing 
effectually to prevent the formation of moisture ; thus confirming 
the observation of Dr. WELLs. 
On another night, favourable to the copious formation of dew, 
B 2 
