24 ROUND THE YEAR 



snow in the vacuum of a water-barometer. Muncke 

 took an exhausted glass bulb and set it, during frost, 

 in the open window of a room, which though not 

 heated, was warmer than the outer air. A little ice 

 had been allowed to form on one side of the interior 

 of the bulb, and this was turned towards the room. 

 Before long the invisible water-particles passed into 

 vapour, and crossing the bulb formed a loose mass of 

 perfectly formed crystals on the opposite side. 



Snow, as it lies on the ground, contains much air. 

 Its density is only one -tenth or one-twelfth that of 

 water. Nordenskiold remarks that even below freez- 

 ing point snow may contain so much water as to 

 drip. 



In ancient and mediaeval times it was believed that 

 long-continued and severe cold could squeeze all the 

 liquidity out of water, and that the permanently solid 

 rock-crystal was formed upon the Alps in this way. 

 Rock-crystal is now known to be crystallised silica, 

 which nearly always takes the form of six-sided 

 prisms or pyramids. 



Why is snow white ? Water, ice, glass and other 

 transparent bodies are not white. But water is 

 white when broken into spray or foam. Ice and 

 glass becomes white when pounded or filled with 

 small air-bubbles. Leeuwenhoeck, two hundred 

 years ago, showed that milk owes its whiteness to 

 minute globules of oil suspended in a watery fluid. 

 A body is white when it reflects much white light. 

 Transparent bodies reflect some light from their 

 surfaces, but allow a great deal to pass through. The 

 more they are broken up, the more numerous do the 



