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 



