Page:Popular Science Monthly Volume 92.djvu/330

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��Popular Science Monthly

��further improbable. The thickness of the mica sheets has been so proportioned to those of the metal leaves that when a hole is burnt through the dielectric, a

���Construction of the casing for a conden- ser with lead-in terminals attached. The dotted line shows the protective cover

larger hole is burnt through the foil. Hence, in this condenser, two oppositely charged pieces of foil cannot come together through the hole made by the leaking currents. The condenser is truly eelf-healing.

As a last precaution against its being burned out by a short circuit, the gen- erator has the pair of protective con- densers shunting it. For these condensers, the Navy officials have also adopted a Dubilier invention, in which two of their condensers are placed. Besides its re- liability, the Dubilier device is also fool- proof. For, as the diagrams show, should their condenser be removed from the

��GENERATOR

���Hook-up showing positions of condensers in the line and how the connections would not be complete without them

circuit, the generator connections would not be complete until another box of protective condensers is connected with the circuit.

��Increasing the Range of the Ground Wireless Station

IN experimenting with inductive coils, placing them with the buzzer in the ground circuit, to see if increasing the inductance would not send larger currents into the earth, it was found that the sending range could be increased in this way to a considerable extent.

First, the contact connections of the buzzer were changed as shown in the diagram. The secondary of the sending coil was connected between the buzzer contact and the buzzer coils, and to vary the inductance, the laminated iron core was moved in and out. For some stations, of course, the ordinary variable radio loading coil will do the trick just as well.

Naturally, the sending range will be largest when the buzzer is vibrating well and the maximum current is sent into the

��� ��Considerably increasing the sending range of a ground wireless station, by the use of an induction coil placed with the buzzer

ground. Therefore the inductive coil should be tuned as in radio work, until the ammeter in the earth circuit registers the largest current. — E. T. Jones, Chief Electrician, Radio, U. S. N. R. F.

Where Fiber May be Used as a Fire- proof Material

FIBER is an almost fireproof material. Almost — for it will burn. But, un- less it is kept on fire by some outside source it will go out, and it requires a very hot flame to ignite it. So, when anyone wants to use fiber in a situation exposed to heat, he can do so. There is little danger of its burning except when it is in the direct path of a flame. The close texture of this material prevents a flame from taking hold unless forced by a draft.

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