Page:Popular Science Monthly Volume 47.djvu/659

Rh, and they course across the sky at higher speed than man can travel. A locomotive can travel a mile in thirty-seven seconds, a fast yacht in about twice that time, and a swift torpedo boat in one hundred and ten seconds. The upper clouds move with an average velocity of a mile in thirty-six seconds, and have been observed moving as rapidly as a mile in eighteen seconds. Equally remarkable are the plastic walls of these aerial reservoirs. No courses of heavy stone and mortar are to be found; but in their stead drops of water so minute that a thousand of them side by side would not extend farther than one inch. If the temperature



was low during the building of the cloud, the water drops are changed into ice spicules and snowflakes.

From such reservoirs the rain falls as a rule harmlessly. A collapse, which rarely occurs, is known as a cloud-burst. Then, the deluge destroys life and property, sweeping all before it.

If we were able to control the valves and vents of this tremendous pump-reservoir, we could cause rain at will and shut off the downpour at pleasure. But hardly yet may we hope to master the rain. Rain-makers of our time bang and thrash the air, hoping to cause rain by concussion. They may well be compared to impatient children hammering on reservoir walls in a vain endeavor to make the water flow. Rain-control is a scientific possibility. Successful rain engineers will come in time, we