X uyiiiLii Kjiiiiti.1 xtxijuimif 



lines of force passing through both, and 

 it should then be endeavored to obtain 

 the maximum flux that a current can pro- 

 duce; that is, to arrange a circuit with 

 the least possible magnetic resistance. 



Moonet 

 cosringX 



ng.io 



General form of a large iron-clad lifting- 

 magnet used with a crane or lift for a hoist 



As a general rule, it will be found ad- 

 visable to make the thickness of the coil 

 about equal to that of the core; to make 

 the yoke just long enough so that the 

 coils will not interfere with each other 

 when placed in position ; and to make the 

 core long enough to accommodate the 

 necessary wire. In all coil winding proper 

 insulation must be provided to prevent a 

 short circuit. The kind of insulation de- 

 pends on the size and use of a magnet. 



In Fig. 8 is shown a cross-section of an 

 electromagnet, showing the coils sur- 

 rounding the core and a general scheme of 

 the lines of force existing in such a mag- 

 netic circuit. The armature is shown out 

 of contact with the magnet and con- 

 siderable leakage flux is depicted. If 

 the armature is brought into contact 

 with the core, it will not only reduce this 

 leakage, but it will increase the flux of the 

 magnet by lowering the magnetic re- 

 luctance of the circuit. 



A few of the principal forms of electro- 

 magnets, including the horseshoe magnet, 

 the electro-bar magnet, and the iron-clad 

 magnet are shown in Fig. 6, 9 and 10. 



The Sleeper Must Get Up to Stop 

 the Alarm 



THE growing habit of switching off 

 the alarm clock and then sleeping 

 a while longer made one commuter miss 

 his train many times. He very easily 

 overcame this difficulty, however, by 

 making an attachment to his bed springs, 

 as shown in the illustration, that com- 

 pelled him to get up to break the electric 

 current. 



A simple frame was made of two brass 

 spring pieces, stretched lengthwise of 

 the bed, one on each side and just under 

 the springs, with a third piece connecting 

 them about 2 ft. from the head. These 

 wires were properly insulated from the 

 bed frame with pieces of fiber attached in 

 the line as shown at A and B. A small 

 turnbuckle C was used to keep the line 

 taut. 



A cheap clock made the electric con- 

 nection at the time set, and a couple of 

 dry batteries completed the device. The 

 connections were simple, one wire was 

 attached from the battery, through the 

 bell to the bed springs, the other from 

 the battery, through the clock to the in- 



The weight of the sleeper makes the con- 

 tact for the circuit on the bed springs 



sulated frame. The clock turned on the 

 current at the time set. The weight of 

 the sleeper caused the springs to touch 

 the frame, as shown by the dotted line, 

 so the bell rang and kept on ringing until 



he got up. — J. K. BURRELL. 



