of Dew on Metallic Surfaces. Y 
the last-mentioned philosopher among the substances that are even 
more productive of cold than wool*. Or it is possible that the 
breeze may have subsided, and the circumstances of temperature 
become such as to have allowed the deposition of dew on the 
paper, but not of its re-formation on the silver. 
Dr. Wells has also remarked +, that when dew forms upon me- 
tals, it ““ commonly sullies only the lustre of their surface ; and that 
even when it is sufficiently abundant to gather into drops, they are 
almost always small and distinct.” This observation, however, re- 
quires some limitation ; since, on nights that have been more than 
usually cold, and when the quantity of moisture in the air has been 
abundant, I have observed the dewy particles deposited on metals 
to attain a considerable magnitude ; and examples have even oc- 
curred of polished tin surfaces being completely covered with thin 
sheets of water, the result of the junction of the innumerable minute 
particles deposited on them. 
On one night, equal squares (their linear edges being one inch 
and half) of lead, zinc, brass, copper, and tin, were laid on a 
large plate of glass, and presented to the influence of a clear sky. 
At sunrise the next morning, the particles of dew on the different 
surfaces were found of variable magnitudes ; those on the lead being 
the largest, and of the size represented in fig. 7. Those on the zine 
were next in magnitude, as denoted in fig. 8; and the particles on 
the brass were still smaller, but much more numerous, as in fig. 9. 
The copper and tin, particularly the latter, seemed only to have had 
the lustre of their surfaces just dimmed, by the abundant moisture 
of the air. Lead, therefore, was at one extreme of the series, and 
tin at the other ; brass holding a middle rank between the two. 
- This relation, however, between the particles on lead and brass, 
was inverted on another night, when equal squares were laid on 
the recently cut herbage, the particles on the brass being of the size 
represented in fig. 10, and those on the lead as denoted in fig. 11, 
As the plates of metal were the same in both cases, it is reasonable 
* Page 21, Essay on Dew, by Dy, Wet1s, second edition, 
} Page 21, second edition, 
