1353. That water exists in the atmosphere is easily proved. If some of the salt, called muriate of lime, which has been just heated red, be exposed to the air, even in the driest and coldest weather, it will increase in weight, and become moist; and in a certain time will be converted into a fluid. If put into a retort and heated, it will yield pure water; will gradually recover its pristine state, and, if heated red, its former weight; so that it is evident that the water united to it was derived from the air. That it existed in the air in an invisible and elastic form, is proved by the circumstances, that if a given quantity of air be exposed to the salt, its volume and weight will diminish, provided the experiment be correctly made.