Page:Popular Science Monthly Volume 92.djvu/647

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��electricity it has on either plate, divided by the potential difference between the plates. A condenser would, therefore, have a capacity of unity in the practical system of units if it would hold a quantity of one coulomb, (the quantity of electricity trans- ferred when a cur- rent of one am- pere flows steadily for one second), at a difference of potential of one volt. Such a ca- pacity is called a farad. This unit represents, how^-

ever, an enormous capacity as compared to those met with in practice, so that it is usual to express capacities in micro- farads, (m.f.). Thus, one m.f. = 0.000001 farad = farad ^ 10*^ = farad x 10"^ But, whenever the general equation is used, the capacity must always be re- duced to farads.

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A number of plates made up into sets

��Securing Wood or Metal Molding to Plaster Walls

THE electrician will find, when putting up wood or metal molding, that by drilling two holes, A, 1 in. apart, instead of one hole, every 3 ft., that not only will time be saved but the molding Vvdll be more secure. The reason for this is that if the hole B was used and the screw went through the plaster between the laths, it

���Two holes drilled close together into the molding hastens the work in putting it up

would be a simple matter to put a screw in hole C and to strike a lathe into which the screw could easily be fastened.

��Now We Reach the Philippines Directly by Wireless

THE last link in a long chain of wire- less stations, reaching from Arling- ton, near Washington, to the Philippine Islands, was recently forged. Cavite, this latest station, situated near Manila, has been building for some time. At its opening Admiral Knight, commander of the Asiatic fleet, sent a message of greeting to Secretary Daniels. In his reply the Secretary commented upon the ease with which our warships in Asiatic waters can now be reached. The chain of sta- tions consists of Arlington, Darien, San Diego, Pearl Harbor, and Cavite.

A Small Storage Battery Made With a Sponge

A STORAGE battery can be made from two lead plates and an old sponge, that will give good service for lighting a small lamp or running small motors.

The battery is made with a one- pint glass fruit jar.

A, two lead plates

B, Y?, in. in diame- ter and as long as the jar, are bent to set opposite each other, each cover- ing one-fourth the inside circumference of jar, A large coarse sponge C is obtained which must be thoroughly cleaned and dried. Then obtain a piece

of lead, and with a coarse file cut off enough filings to fill every pore in the sponge. When this is done, sprinkle the filings on the sponge which is in the jar between the plates. Be careful to keep the filings from falling out of the pores. The sponge must fit tightly against the walls of the jar to hold the filings in. Next fill the jar with one part sulphuric acid to seven parts of distilled water.

If this battery is charged in series with a 16 C. P. lamp on 110 volt D. C. line it will give 2 volts and 14 ampere hours. — William Harrier.

���A 16 c. p. lamp must be used while charging

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