It is evident that water exists in the atmosphere in abundance, even in the driest seasons, and under the clearest sky. By the experiments of Saussure, it appears, that a cubic foot of atmospheric air will hold eleven grains of water in solution. From this property of the air we derive many advantages. It has a tendency to preserve every thing on the face of the earth in a proper degree of moisture. It appears, from the experiments of some aëronauts, that the air is much drier in the higher regions than it is near the surface of the earth. When two opposite currents of air meet, of different temperatures, the vapors are sometimes condensed thereby, and rain ensues. It may be remarked, that if the temperature of our atmosphere had been 212, or upwards, rain could never have fallen on the earth; for the water taken up by evaporation would have been converted into a _permanently_ elastic fluid. Such is the necessity of rain, that it _alone_ not only affords a proper degree of moisture to the vegetable creation, but is of service in bringing the soils into a fit state to perform their office. Dry earth of itself is ineffective; but when _moistened_ it has the property of decomposing atmospheric air, and of conveying its oxygen to the roots of those plants which vegetate within it. We are indebted to Humboldt for the knowledge of this fact. It is impossible ever to contemplate the various ways in which the different operations of nature are made to correct and balance each other, without being struck with the infinite comprehension of the Divine Mind, which could thus foresee the tendency of every law which it was about to establish. How many cases are there in which the slightest oversight would have produced the destruction of the world! The effects of vapor have furnished a new moving force to mechanics, says Haüy, which it required no ordinary genius to have created, and to have measured its energy. This science, during a long time, had only employed water as a moving force, by availing itself of its natural course, or by judiciously managing its fall, so as to subject it to the operation of machines which is regulated by an impulsion continually renewed. The experiments made upon the force of water reduced to vapor, gave birth to the idea of applying that vapor so much the more advantageously to the same purpose, because independently of its great energy, it may be transported wherever it is called for by the interests of commerce and industry.