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Page:Popular Science Monthly Volume 89.djvu/433

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Pupidur Science Moiiflih/

��419

��a helper tlirouvili the large door, and the

operator has his head and arms strapped

into a head-dress constructed so that

the curtain forms the front of the hopper.

This curtain is attached to shding metal

doors moving

horizontals,

allowing the

workmen to

move from side

to side at will

by the pressure

of their elbows

upon the metal

leaves.

The head- dress is con- structed to al- low a free pas- sageofairabout the head and through the fine copper gauze into the sand blasting de- partment. The strong suction in the sand blasting depart- ment sets up a sufficient vac- uum to cause

the fresh air to circulate around the head of the workman and the copper gauze into the sand blasting department. This affords a constant supply of fresh air for the operator, while the inrush of air clears the copper gauze and assists the vision of the operator. In practice the amount of fresh air drawn through this head-dress is so great that the workman wears a shield on the back of the head as a protection from the draft.

In operation a considerable econom\- is effected through the use of a much smaller system of exhaust and dust col- lecting. Less sand is required and the total saving of power and material is increased. A battery of twehe of these outfits is at work in an open room, and no discomfort is experienced b\- either the operator or others working in the xacinity. The same principle is applied to sand blasting automobile bodies.

���Sand Blasting Automobile Parts with the Modem Head-Dress. The Fresh Air Is Supplied Under Pressure

��Why Not Make Rain Work? A Chance for a Rain Motor

THERE have been numerous at- tempts at utilizing the energ>- of the sun and the tides, but it is doubtful

whether the en- ergy of rain has e\er been con- sidered. A little figuring, how- ever, will con- \ince one of the enormous force yet un- harnessed.

One inch of rainfall is not uncommon in this country, \et ever\' time this happens the earth is moistened with a paltry 113 tons of water to the acre, or 72,480 tons per square mile. The annual average rainfall the world over is estimated at 36 inches. Using this value and our first figure, we arrive at the astonish- ing result that the average rain fall- ing on one square mile in a year is 2,609,280 tons in weight. How small is this figure, though, when we think of parts of British India where the precipi- tation is given at 610 inches.

.\ law of ph\sics says that work equals force multiplied b\- the distance through which it acts. Let us consider the energy of all this weight of water falling from the clouds. The height of clouds is estimated at from two to three miles, but to allow for seasonal variation and the lower height of rain clouds let us take 2,000 feet. Using this figure we find that the average work done by falling rain in 24 hours is 22,320 foot-tons per acre — assuming our annual average rain- fall of thirt>-six inches distributed uni- formly throughout the \ear.

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