See that article (Encycl.), where we have endeavoured to account for snow's contributing to the preservation and growth of vegetables. It must be con- fessed, however, that if snow possessed only the proper- ty of preserving vegetables, and of preventing them from perishing by the severity of the cold, it is not at all probable that the ancient philosophers would have con- sidered it as depositing on the earth nitrous salts, as they might have ascertained, by a very simple experi- ment, ment, that it contains none of that salt; for they did not ascribe the same property to rain-water, but they remarked that snow burnt the skin in the manner of acids, as well as other bodies immersed in it. Being induced to conclude that there was nitre in the air, it was natural that they should ascribe to this nitre the burning qualities of snow, and consequently its influence on vegetation.

Such reflections induced Morveau, alias Citizen Guyton, to employ J. H. Hassenfratz to inquire into the cause of the difference of the effects of snow and rain-water on various substances. Hassenfratz found that these differences are occasioned by the oxygenation of the snow; and that these effects are to be ascribed to a particular combination of oxygen in this congealed water. He put 1000 grammes of snow in a jar, and 1000 grammes of distilled water in another. He poured into each of the jars an equal quantity of the same solution of turpentine. He placed both the jars in a warm temperature; and after the snow melted, he remarked that the dye was redder in the snow water than in the distilled water. He repeated this experiment, and with the same result. He put into a jar 1000 grammes of distilled water, and into another 1000 grammes of snow. Into each of the jars he put 65 grammes of very pure and clean sulphate of iron. In the first, there was precipitated 975 grammes of the oxyd of iron, and 900 grammes in the other. As the oxyd of iron was precipitated from a solution of the sulphate by oxygen, it thence follows, that the snow contained more oxygen than the distilled water; and it follows, from the first experiment, that this quantity of oxygen was considerable enough to redden the tincture of turpentine.

It is fully demonstrated by these two experiments, that snow is oxygenated water, and that it must consequently have on vegetation an action different from that of common ice. The experiments of Dr Ingenhousz on the germination of seeds have taught us, that the presence and contact of oxygen are absolutely necessary for the plant to expand. They have shown also, that the more abundant the oxygen is, the more rapidly will the seeds grow. Most plants suffered to attain to their perfect maturity shed on the earth a part of their seed. These seeds, thus abandoned and exposed to the action of cold, are preserved by the snow which covers them, at the same time that they find in the water it produces by melting, a portion of oxygen that has a powerful action on the principle of germination, and determines the seeds that would have perished to grow, to expand, and to augment the number of the plants that cover the surface of the earth.

A very considerable number of the plants which are employed in Europe for the nourishment of men, are sown in the months of September, October, and November. The seeds of several of these germinate before the cold commences its action upon them, and changes the principle of their life. The snow which covers the soil, acting on the germ by its oxygenation, obliges them to expand, and to increase the number of useful plants which the farmer and gardener commit to the earth, and consequently to multiply their productions.

Here, then, we have three effects of snow upon vegetation, all very different, which contribute each separately to increase, every year, the number of our plants; to give them more vigour, and consequently to multiply our crops. These effects are: 1. To prevent the plants from being attacked by the cold, and from being changed or perishing by its force. 2. To furnish vegetables with continual moisture, which helps them to procure those substances necessary for their nutrition, and to preserve them in a strong healthy state. 3. To cause a greater number of seeds to germinate, and consequently to increase the number of our plants.