Page:Popular Science Monthly Volume 90.djvu/388

 372

��Popular Science Monthly

��Making a Stage Ocean with Green Silk and an Electric Fan

ATTEMPTS made to devise apparatus L by which the effect of a heavy sea can be obtained on the stage without actually employing. water have been somewhat un- successful. Ordinarily a large canvas is employed, painted to represent waves and moved by machine or by hand beneath the canvas, Stereopticon pictures and colored lights have been utilized to make the effects more reahstic. All these at- tempts have not only been expensive and cumber- some but have proved unsatisfac- tory. They lacked real- ism.

Ida May Fuller, of New York

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��Festoons of light-weight silk, sea-green in color, are supported by wire netting and waved by the air currents from the fan

��city, has obtained satisfactory results on the stage by means of an openwork support, preferably of light, white netting, to which is attached in festoons on the front side a fabric such as a fine translucent silk, which reflects light and which is of such texture as to be easily waved back and forth by an electric fan or by hand.

Water-green colored silk produces a sat- isfactory illusion, without any external lighting effects, regardless of whether the motion of the waves is made by stage hands moving the support or whether an electric fan is used. When it is desired to show figures or objects beneath the water the figures are placed beneath the projecting light and behind the support.

��attached has been employed to generate the electricity. William H. Chapman, of Portland, Maine, applies the contact prin- ciple of the iron pulley and belt instead of the principle of friction in static gene- rators.

In his machine the usual friction pads give place to a trough of mercury, analogous to the iron pulley. Not only is an unpre- cedented mechanical efficiency obtained but

from an elec- trical stand- point the high p o - tential effects are of an order not heretofore attainable with friction apparatus.

A glass plate eight inches in diameter, making eighty complete rev- olutions a minute and dipping into

�� ��a mercury trough to a depth of one and one half inches, without induction plates, will develop a potential of 9,000 volts on comb points, arranged to collect the charge at the top of the plate. The application of induction plates close to the revolving plate, at the point where it leaves the mercury, raises the potential to 13,000 volts or more on the comb points and gives sparks three- quarter inch long. This is still further increased by covering the induction plates with k thin sheet of rubber or glass.

��ROUNDED TO PREVE.NT BRUSH DISCHARGES

��CHARGE COLLECTING TEETM

��GLASS DISC

��A Frictionless Contact Generator of Static Electricity

WHEN two dissimilar substances are pressed together and then separated, one acquires a positive charge and the other a negative charge. A leather belt running on an iron pulley is an illustration of this. The belt) acquires a negative charge at the point of separation from the pulley and the pulley a positive charge.

Hitherto, with static generators, a mov- ing plate of glass with frictional rubbers

���TROUGH

��DUCTION PLATE FOR KEEPING DISC DISCHARGE LOW NEAR MERCURY AND DISC CONTACT POINT

��In this machine a trough of mercury is employed to generate electricity by contact

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