DR. C. B. PLOWRIGHT ON SILVER THAW AND GLAZED KROST. 347 
streets (High Street) has within the last year or two had its granite- 
cube pavement replaced by asphalt ; this is apt at times to be so 
slippery that many persons driving valuable horses avoid passing 
down it. Curiously enough this street was the least slippery in the 
whole town. On the Gaywood road the silver thaw was very well 
developed; between Gaywood corner and the Easb Gates, a distance 
of about half-a-mile, eleven horses fell during the evening. The 
blacksmiths had to re-open their shops, and did a brisk business in 
“ turning up,” or “ roughing ” horses. During the evening two 
children were treated at the Hospital for scalp wounds, caused by 
slipping on the ice ; and later a man was admitted with concussion 
of the brain, and a woman with a fracture of the fibula from the 
same cause. 
During the night the rain ceased, and it again froze, so that on 
the morning of the 21st we had an excellent illustration of a glazed 
frost. It was the more noticeable owing to the previous absence of 
snow or ice on the roads, and for the suddenness with which the icy 
coating had developed upon them. 
The explanation of this phenomenon is given by Mr. Scott* in 
these words : “ The glazed frost is really the frozen surface which 
is occasionally produced at the beginning of a thaw if a warm wind 
suddenly sets in. The damp air, passing over the ground, of which 
the temperature is exceedingly low, has its moisture deposited in 
a solid form, and all objects on which this deposit takes place are 
covered with a sheet of ice.” 
Instances may commonly be observed on walls where the porous 
bricks become coated with ice when a long frost is breaking up, but 
as there is generally more or less snow upon the ground, the phe- 
nomenon is not so noticeable as it was upon the present occasion. 
Sometimes glazed frosts cause a great amount of injury to trees by 
breaking their branches from the weight of ice deposited upon them. 
On the morning of the 21st, the ice-coating on the pebble 
pavements in some of the streets was found to have become 
detached during the night from the convex surface of the stones. 
This was effected by the expansion of the ice as it was deposited, 
lifting itself from the stone because it was unable to expand 
laterally, owing to the proximity of the neighbouring pebbles. 
* ‘ Elementary Meteorology.’ Robert H. Scott, F.R.S., 4th edition, 1S87, 
p. 115. 
