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. 



All the specialized knowledge and information of the editorial staff of the Popular 

 Science Monthly is at your disposal. Write to the editor if you think he can help you. 



