Once it took a long time for molasses to drain out of a hogshead of damp sugar.  Now it is put into a great tub, with holes in the side, which is made to revolve rapidly, and the molasses flies out.  In the best laundries clothes are not wrung out, to the great damage of tender fabrics, but are put into such a tub and whirled nearly dry.  So fifty yards of woolen cloth just out of the dye vat—­who could wring it?  It is coiled in a tub called a wizard, and whirled.

Muddy water is put through a process called clarification.  It is the same, except that there are no holes in the vessel.  The heavier particles of dirt, that would settle in time, take the outside, leaving perfectly clean water in the middle.  A perpendicular perforated pipe, with a faucet below, drains off all the clear water and leaves all the mud.  Milk is brought in from the milking and put into a separator; whirl it, and the heavier milk takes the outside of the whirling mass, and the lighter cream can be drawn off from the middle.  It is far more perfectly separated than by any skimming.

A rotary snowplow slices off two feet of a ten-foot drift at each revolution, and by centrifugal force flings it out of the cutting with a speed that a hundred navvies or dagos cannot equal.

ONE PLANT HELP

A thousand acres of land on Cape Cod were once blown away.  This wind excavation was ten feet deep.  It was not an extraordinary wind, but extraordinary land.  It was made of rock ground up into fine sand by the waves on the shore.

In all the deserts of the world the wind blows the itinerant sand on its far journeys.  If the wind is moderate it heaps the sand up into little hills, some of them six hundred feet high, around any obstruction, and then blows the sand up the slanting face of the hill and over the top, where it falls out of the wind on the leeward side.  In this way the hill is always traveling.  In North Carolina hills start inland, and travel right on, burying a house or farm if it be in the way, but resurrecting it again on the other side as the hill goes on.  Anyone may see these hills at the south end of Lake Michigan, as he approaches Chicago, west of San Francisco, all along up the Columbia River—­the sand having come on the wings of the wind from the coast.

But to see the whole visible world on a march one needs to go to a really large desert.  The Pyramids and the Sphinx have been partly buried, and parts of the valley of the Nile threatened, by hordes of sand hills marching in from the desert; cities have been buried and harbors filled up.  Many of the harbors of the ancient civilizations are mere miasmatic marshes now.  This is partly in consequence of the silt brought in by the rivers; but where the rivers do not flow in it is because the sand blows in along the shore.  Harbors are especially endangered when their protection from the waves consists of a bank of sand, as on Cape Cod and the Sandy Hook below the Narrows of the harbor of New York.