Page:Popular Science Monthly Volume 92.djvu/968

 952

��Popular Science Monthly

��E.M.F.'s, and power on both D.C. and A.C. circuits.

The permeability bridge, an apparatus designed for the determination of the magnetic densities of iron corresponding to given magnetizing forces.

The hysteresis meter used for measur- ing the hysteresis in sheet iron and steel.

The Wheatstone, or slide-wire, bridge used for the accurate determination of re- sistance.

The above discussion includes the principal types of meters and instruments used in the testing of electrical apparatus. While there are other meters on the market, it will generally be found that they are simply modifications of one or the other of the above typical meters, or are designed for very special or limited use.

{To he continued)

��I

��A Combined Electric Night-Bell and Flash-Light

N rigging up a bell for an invalid it was

��decided to

iplice

��add

��an extra wire and have a flash-light as well as a bell. The bell and light are independent of each other, al- though one of the bell wires is also used for the light and the same bat- teries work them both. The draw- ing shows clearly how to connect the wires.

A pear-shaped push button is used for the bell and connected in the usual way. The flash-light with its reflector is held in place by binding it with adhesive plaster. The switch consists of a piece of spring brass and a round head screw. After all the connections are made, the whole neck of the push button is wound with tape. Pushing the switch lights the light, push- ing the button on the end of the push button rings the bell. Two cells of dry battery will be sufficient to work either the light or bell. — Albert E. Jonks

���Dry cells

��A battery lamp on push button

��A Thimble Used as a Ferrule on a Tool Handle

AN old thimble makes an excellent L ferrule for a small screwdriver handle or a similar tool. A notch is filed in the thimble end to admit the rectangular shank of the tool like a flat file. Round shanks may be fitted into a drilled hole or the thimble end cut off entire- ly for tools like an awl or chisel. The small inden- tations will hold firmly in the wood if the end is fitted snugly; however a prick punch or a small hole with a brad driven in will keep the thimble in place on the handle. The round end of the thimble makes a very neat fitting ferrule that is not obtainable in the ordi- nary kind. — James M. Kane.

���Thimble on wood handle

��A Self -Translating Telegraph Line for Amateurs

THOSE electrical experimenters who have possessed a private telegraph line know what fascination there is in communicating with a friend by this means and also know what a wonderful possibility of misunderstanding there is in such a device when the operators have only a speaking acquaintance with the

���Forty divisions around the face of the wheel for necessary alphabet characters

standard telegraph code. There is no doubt that many more amateurs inter- ested in electricity would have such a line

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