Why is snow a warm covering for the earth?
Because the air in the snow makes it a poor conductor of heat, so that it prevents the warmth of the earth from passing off into the air. Snow is, therefore, a protection to the plants, and prevents their being frozen by the cold weather of winter.
What is hail?
Drops of rain, when frozen, are called hail.
How is hail formed?
The rain-drops are frozen as they fall through the air; hence, the hail-stones of winter are no larger than the rain-drops.
When have we dew?
When the air in contact with the earth or the plants is cooled, its vapor is condensed into dew.
When have we frost?
When the air in contact with the earth or the plants is cooled below thirty-two degrees, its vapor is condensed into dew, and the dew is frozen into frost.