180 GLAISHER, ON SNOW CRYSTALS. 



future opportunity to extend my acquaintance with the 

 separate varieties which each class included. In accordance 

 with the law that water crystallizes at an angle of 60', the 

 base of every figure was a hexagon of six rays. These rays, in 

 passing through successive stages of crystallization, become 

 encrusted v/ith an endless variety of crystalline formations, 

 some consisting of thin laminae alone, others of solid but trans- 

 lucent prisms, heaped one upon another, and otheis gorgeously 

 combining laminaB and prisms in the richest profusion. 



At the beginning of the frost, the kind which was most 

 common, and attracted universal attention, was of simple six- 

 rayed stars, with a central molecule of snow. These fell in 

 clusters of several in a group, and in their descent had the 

 appearance of tolerably large and fleecy snow-flakes. The 

 ground had for some days been covered with snow ; but where 

 the soil was visible, they lay like ravellings of fine white 

 cotton, knotted here and there, an effect produced by the 

 large white molecule, the centre of each star. I chanced 

 to be in the neighbourhood of Abbey Wood, when a shower 

 of these fleecy-looking groups began to fall. The air was 

 calm, the snow lay upon the ground, and the sky was over- 

 cast. The surface of the snow was soon covered with clusters 

 of these figures, beautiful in their simplicity. They were 

 certainly 4-lOths of an inch in diameter, and could be readily 

 distinguished. The temperature at this time was at or near 

 32°. After falling about a quarter of an hour, they became 

 intermingled with a variety of very complex crystals. Some 

 of these last exhibited all the rigidity but harmonious pro- 

 portions of geometric figures ; others the fanciful luxuriance 

 of the fronds of the Lady fern ; others, again, exhibited an 

 arrangement of trefoils, and some there were, with pinnae of 

 unequal size, three being large and fully-developed, of fern- 

 like character, and three being little more than spicule. The 

 air, during the continuance of the shower, was considerably 

 cooled, and was at its coldest when these beautifully-varied 

 figures were falling. Towards the close of the shower, fleecy 

 groups of stars were again prevalent, the air was less cold, 

 and half an hour after, when the shower ceased, the sun was 

 endeavouring to penetrate the gloom which before prevailed. 



I will endeavour briefly to describe the departures from 

 the ordinary or primitive form. 



On February 8, the day of the first heavy and continued 

 snow, I secured drawings of some of the most remarkable 

 figures which fell in numbers throughout the day, and accom- 

 panied the snow. The minimum temperature of the preceding 

 night had been 29° ; at 9 o'clock the thermometer in air was 



