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The Museum Gazette 



SOME OF THE PHENOMENA OF FROST. 



Cat-ice is ice which has air under it, and which is so 

 thin as to be hardly strong enough to support a cat. It is 

 formed when a night-frost follows soon after rain. The 

 puddles, cart-ruts, &c, are then full of water. The surface 

 under the influence of a cold wind suddenly freezes. Mean- 

 while the water has been soaking into the ground and leaves 

 a layer of ice no longer supported below. The ice now pro- 

 tects from the wind the water remaining under it and prevents 

 further freezing. Cat-ice is rarely translucent, but looks more 

 or less opaque and white. This appearance is in part illusory 

 and caused by what is seen beneath the ice, but in part it is 

 real, and caused by the formation of white crystalline particles 

 of hoar frost on the under surface of the ice. 



Hoar Frost, or white frost, is produced under two somewhat 

 differing conditions. Its most common state, that in which 

 the fields and ground become white, is caused by the freezing 

 of dew which has settled upon the points of the herbage, 

 leaves of trees, or fragments of stone. It occurs when the 

 nights are clear, still, and cold. As soon as the temperature 

 sinks below dew point, moisture is deposited, and at once 

 congeals in a crystalline condition which looks white. A 

 liberal white frost always implies a preceding clear night 

 during which radiation has been free. The hedges, bushes, 

 &c, are always more or less implicated when hoar frost forms 

 on the ground. There is, however, another form of white 

 frost of much higher glory which results from the sudden 

 freezing of a wet mist. For this to occur the air must be 

 heavily laden with moisture, the sky hidden by fog, and the 

 onset of cold, sudden and without wind. Every tree is drip- 

 ping with water, and all the water becomes white ice. The 

 process may go on for hours, and festoons of glittering white 

 with fragile icicles in them result. If, after such a night, the 



