OUR ICE-SUPPLY AXD ITS DANGERS. 673 



downward inch by inch. l>ut this condition of affairs, quite ideal 

 from tlie standpoint of the ice-farmer, is apt in this region to be eva- 

 nescent. If the grip of the cold relaxes by day, the formation of ice 

 may stop, and even a film of that already made may melt away in the 

 water beneath ; but at night again another layer may be added, and 

 so, with many halts, retreats, and slow advances, little by little the ice- 

 mass thickens. But who would imagine that, written in the ice, as plain- 

 ly as the sequence of geologic ages is written in the rocks, is the record 

 of these alternate victories of heat and cold as they contended for the 

 mastery of the water during the winter days and nights? Strange as 

 it may seem, the record is there, however, and, stranger yet, is written 

 in air. Look at the edge of a cake of ice which has formed in com- 

 paratively still water during such alternations of temperature as are 

 common in our winters, and you will be very apt to see a series of 

 bands of transparent ice, between which lie layers of tiny air-bubbles. 

 In still water, when the ice for any reason stops forming for a time, 

 bubbles of air from the water or from the bottom are apt to rise and 

 collect beneath the ice, and when the, freezing again begins they are 

 entangled and held fast between the old and the new ice-layers, a per- 

 manent record of the relaxation of the thrall of the cold long enough 

 for their collection. In running water such bubbles are apt to be 

 swept away, and the ice remains transparent. 



While the ice is thus forming the ice-farmer looks on, his spirits 

 rising in inverse ratio to the height of the thermometer. To the 

 vagaries of the temperature he must reconcile himself as best he may. 

 But let his btte noire, the snow — if so violent an antithesis be permis- 

 sible — appear, and he will be on the alert at once. The snow-flakes, 

 delicately adjusting themselves to one another as they settle down 

 upon the ice, build up among their crystals myriads of tiny air-cavities, 

 and the whole forms a veritable blanket which hinders radiation. It 

 is warm for the same reason that a down comfortable is — it prevents 

 the escape of heat. Now, what shall our ice-farmer do ? It does little 

 good to swear at the snow, although he usually has recourse to this 

 procedure first. If the already formed ice is thick enough to bear the 

 teams, he may scrape the snow off, and then the freezing can go on. 

 But if not, he sends his men over the field to cut small holes here and 

 there through it ; the water wells up, flows over the top, forming a 

 layer of slush, a good deal of the air is expelled, and the whole freezes, 

 forming a whitish layer which is called snotc-ice. This layer is whitish 

 because of the air-bubbles which it still retains, but it conducts off the 

 heat fairly well, and his crop goes on forming. This opei-ation is called 

 " tapping " or " bleeding " the ice. Ice which has a very thick snow 

 layer is called "fat ice." This snow-ice is not as valuable as clear ice, 

 for householders object to it because they fancy that it is not so pure, 

 and the assurances of the dealers that the impurity is only air appear 

 to have little weight. So the more responsible dealers usually find it 

 VOL. XXXII. — 43 



