ICE ITS FORMS AND FUNCTIONS. 



ICE, DEFINITION OF GENERAL PHYSICAL PROPERTIES OF WATER 

 FORMATION OF ICE ITS OCCURRENCE IN THE ATMOSPHERE : HOAR- 

 FROST, SNOW, AND HAIL ITS OCCURRENCE ON FRESH WATER : 



RIVER, LAKE, AND GROUND ICE ON SALT WATER : ICE-FIELDS, 

 ICE-PACKS, ICE-FLOES, ETC., IN POLAR SEAS ICE ON LAND : SNOW 

 AND SNOW-LINE, AVALANCHES, N^VB, GLACIERS THEIR CHAR- 

 ACTERISTICS ICEBERGS GENERAL RESULTS OF ICE-ACTION. 



THERE is no substance in nature so protean in form, so 

 incessant in circulation, or so multifarious in its functions 

 as water. Now aeriform, now liquid, now solid ; now in 

 the ocean, now in the atmosphere, now percolating the 

 earth's crust, now coursing its surface and hurrying again to 

 the ocean ; now supplying the wants of plants and animals, 

 now wearing down the earth in one part, now accumulating 

 new material in another, and anon locked up, as water of 

 crystallisation, in the mineral structure of the globe for 

 ages. The sum of its existence is change ; the whole course 

 of its history a series of marvels. It is, however, only 

 with one feature of its existence, and with a small portion 

 of its history, that we have to do in the present instance ; 

 though we have necessarily to glance at its general deport- 

 ment under heat, the incessant modifier of its form, and the 

 great propeller of its circulation. 



At ordinary temperatures, as every one knows, water 

 appears in the liquid state ; at high temperatures it passes 

 rapidly into the vaporiform condition, and at low temper- 



