On running streams, these conditions are much modified. In passing over shallows or rapids, where the current is swift, the water remains open and exposed to the air. At these points in its course it parts with its accumulated air and heat very rapidly, a thin vapor or mist being often perceptible in the air at such places, owing to the rapid radiation. The tumbling and turning of the water at rapid shoals materially assists the growth of ice at points below where the current grows gentle. Streams of this character, whose beds are free from accumulations of vegetable mold, or other sources which generate gases, produce clear and sparkling ice of greater thickness than is found on still ponds or lakes in the same vicinity, and exposed to the same temperature.
The Usefulness of Snow.—Snow, as it is well known, is a great impediment to the inroads of frost into anything enveloped by it. A covering of snow on an ice field is a great impediment to the escape of heat from the water, as well as protecting the ice from the direct action of the cold air, and greatly retards the growth of the ice. It is essential to remove this snow as early as practicable, as the ice harvester has always in view a possible thaw or rain, and endeavors to secure his crop at the earliest practicable moment.
Snow, however, in the event of soft or warm weather, is an aid to the ice by protecting it from the direct heat of the sun, and the force of a rain is largely expended in melting the snow. The water and snow on the top of the ice freezes into snow ice as soon as the weather turns cold again. This snow ice is white, being very porous and filled with air, and detracts from the quality of the crop, its thickness depending on the depth of snow on the field, amount of water, and the temperature. At the top of this snow ice, where it merges into the snow, will be found a stiff, crusty layer, more or less firmly united to the ice below, which adds to the difficulty of removing the snow on top. An inch or two of snow ice will lessen the loss by breakage of cakes, in stowing, and the ice also comes out of the house in better shape, and will stand shipping better. It is not so brittle as clear ice, and is homogeneous in its structure, not being readily split in any direction.
Removal of Snow.—Various methods and appliances are in use for the expeditious and economical removal of snow. As soon as the field will bear the weight of a horse, scrapers of various designs are placed at work. If the ice is too thin to support a horse safely, flooding is resorted to. At intervals of six feet, more or less, according to the freedom with which the water rises through the openings, holes are cut through the ice, and the water saturates the lower part of the snow.
FIG. 1. CLEARING OFF SCRAPER.
This helps to thicken the ice rapidly, and, if the weather is cold, it will very soon be heavy enough to support a horse. As soon as this is the case, the scrapers are placed at work. The snow ice thus formed is afterward gotten rid of by planing, if more than an inch or two in thickness. If the snow is light, and not too deep, it is scraped into windrows, by scrapers similar to those in Figs. [2], [3] and [4].
FIG. 2.
