GENERAL REVIEW. 227 



" ice - field " of the sailor, which, when broken up, be- 

 comes his "ice-brash," and either floats away in "floes" 

 and "patches," or is drifted by winds and currents in 

 " packs " and " streams." * The conservative effect of this 

 ice-crust on the 'warmth of the ocean is one of the most 

 providential arrangements in nature maintaining for the 

 water beneath the mean of 39, when in the air above the 

 cold is often sufficiently intense to solidify mercury, whose 

 freezing point is 39, or 39 below zero. Gradually as 

 the ice thickens, it protects more and more the subjacent 

 water ; t gradually as the water in contact with the under 

 surface of the ice is chilled, it becomes heavier, and sinks, 

 its place being taken by a warmer film ; and gradually as 

 the water is converted into ice (it freezes fresh, or only with 

 such brine as maybe entangled in its interstices), the upper 

 film, being salter and denser, descends, and lighter and 

 warmer particles ascend to take its place. In freezing, 

 water, of course, gives but heat, and the heated air-bubbles 

 may often be seen clustering beneath the ice and struggling 

 as it were to escape upwards. Every bubble in this way 



* The names by which the different conditions of sea-ice are known to 

 our whalers and navigators. The "ice-field" or "field of ice " is the 

 unbroken ice of the polar oceans ; when broken up by thaws and storms 

 it becomes " brash-ice ; " when drifted into dense masses it is " pack- 

 ice ; " and when floated away by winds and currents it passes either into 

 solitary " floes," into " patches " of several floes, or into " streams," 

 having a determinate direction. A solitary fragment floating with a 

 considerable portion of its bulk above water is a " hummock ; " and 

 when loaded with debris and chiefly under water it is a " calf." The 

 young ice that is rapidly formed, on the approach of winter, between 

 floes and patches is "pancake ice;" when of greater thickness, and 

 formed in creeks and inlets, it is "bay-ice." These different conditions 

 are also known at a distance by their " blink " or reflection this being 

 clear for field-ice, white for packed, grey for newly formed, and deep yellow 

 for snow. 



t As ice slightly contracts at temperatures under 32, the intense cold 

 of the polar regions only tends to render it more homogeneous and com- 

 pact, and thus to increase still further its powers of protection. 



