417 
of Edinburgh, Session 186S-G9. 
In 1781 Professor Wilson observed in the Observatory Park at Glas- 
gow a cold of — 4° Falir., and in 1780 actually one of — 14° Fahr. 
Dr Guthrie, one of many Scottish physicians of the time who 
settled in Russia, describes in a dissertation read to the Society in 
1789 a remarkable phenomenon he had observed in the thawing of 
thick ice. When ice on the river Neva had been reduced by thaw 
to two-thirds of its thickness, it became so brittle as not to bear 
even the weight of a dog, though still eighteen inches thick. The 
cause he discovered to be that the ice is then composed of solid 
crystals “ like organ-pipes,” about eighteen inches long, and with 
scarcely any cohesion among themselves. This appears a structure 
somewhat analogous on the large scale to the loss of cohesiveness 
among the minute particles of ice, which gives occasion to the 
downward descent of glaciers. 
The only original inquiry in Thermometric Meteorology produced 
to the Royal Society of Edinburgh in its early life, is one of great 
importance in a scientific respect, as well as practically by reason 
of its bearings on atmospherical thermometric observations. This 
is the dissertation well known to learned meteorologists, but lost 
sight of by too many others, of Patrick Wilson, Professor of 
Astronomy in Glasgow, “ On a remarkable cold which accompanies 
the separation of hoar-frost in a clear air.” This inquiry, read in 
1784, and carried on during several previous winters, in continua- 
tion of researches of the same kind communicated to the Royal 
Society of London in 1780 and 1781, is the germ which ultimately 
produced in the hands of Dr Wells the true theory of the formation 
of dew and hoar-frost; and the author approaches so near that 
theory as to create regret that, having stepped on the right path, 
he had not the luck to follow it to the end. Wilson was the first 
to observe the difference in clear frosty weather between the 
temperature of snow, hoar-frost, sand, and many other objects, and 
the temperature of the atmosphere a few feet above. He frequently 
observed a difference of 4°, 8°, 12°, and even on one occasion 16° 
of greater cold on the surface of snow, than in the air four feet, or 
even only two feet and a half above it. He also noticed that this 
difference is always attended with an increase of weight from the 
deposition of hoar-frost ; that the difference is always greatest when 
the atmosphere is clearest and stillest; that wind, even in clear 
