52 
REPORTS OF SOCIETIES. 
six. I noticed that the walls of these ice-cells had formed upon the 
upper surfaces of the wires of the gauze, and were about the same 
thickness as the wires ; that the cells themselves all sloped very much 
—probably at about an angle of 45° with the horizontal piece of gauze 
— and that their axes all lay in the same direction, namely, facing 
that from which the wind blew (N.W., but almost a dead calm, with 
a very steady barometer at about 30’70 s.l.). The length of the cells 
was about lialf-an-inch, though near the edges of the pipe they were 
shorter. The direction of the air flowing through the gauze was 
inwards and vertically downwards, the quantity being about 100 cubic 
feet per minute, the area of mouth of pipe being 50 square inches. 
A thick fog prevailed, but the air temperature was from two to three 
degrees above freezing point, and there had been no frost the night 
before. This peculiar formation of frozen fog seems to me to be 
accounted for in this way :—The cold foggy air being sucked rapidly 
through the meshes of the gauze became so much reduced in 
temperature, due to rarefaction , as to cause it to fall below 32° F., 
and to be converted into hoar frost or ice, and, as long as the con¬ 
ditions remained the same, the ice cells grew outwards or in the 
direction of the in-rusliiug air, coming, as already mentioned, from the 
N.W. I have often observed, too, that long-pointed horizontal crystals 
of hoar frost rapidly form along a door-sill, just beneath the bottom of 
the door, in cold thick-foggy weather during a calm. When this is 
the case a strong current of air is passing through the chink from the 
open air. In these instances also the ice-needles grow outwards, or in 
the direction whence the air comes in. I suppose here, again, we 
have the same cause, namely, reduction of temperature, causing ice to 
form as described. But whether such objects as spiders’ webs, long 
grass, twigs, sharp edges of posts, telegraph wires, Ac., are directly 
concerned in the formation of hoar frost or not I am scarcely able to 
say, unless it be that they cause a local lowering of temperature and, 
therefore, a deposition of ice particles. Whether there is anything 
new in this idea of mine I cannot say, but I do not find the (?) theory 
in print. 
Overseal, 14th January, 1888. W. S. Gresley. 
Reports of Societies. 
BIRMINGHAM NATURAL HISTORY AND MICROSCOPICAL 
SOCIETY. —Geological Section.— January 17tli. Chairman, Mr. T. 
H. Waller, B.A., B.Sc. Mr. Waller, B.A., B.Sc., was re-elected 
President of the Section; Mr. Udall, F.G.S., was re-elected Secretary 
of the Section; Mr. Thos. E. Bolton, son of the late lamented 
Curator, was unanimously elected a life member. Specimens were 
exhibited by Mr. Mantell of Upper Cambrian i*ocks showing Oleni in 
black shales, and Dictyonema in grey shales. A paper was read by 
Mr. Waller—“ Notes on Serpentine Rocks,” illustrated by microscopic 
preparations, including Picrite, Scyelite, Ac. 
