Electricity. 331 



action in a magnet which prepares the way for and which precedes the 

 the drawing of a body to it, is the creation around such body of the 

 magnetic whirls and the consequent formation in it of a central line of 

 force, the ends of which constitute its poles, or tension extremities. And 

 since positive attracts negative, and vice versa, the negative pole of 

 the attracted bod}' will be found next the positive pole of the magnet, 



FIG. 143. 



FIG. 142. 



FIG. 142. Horse Shoe Electro Magnet. 

 M. .^oft-iron bent bar. 

 A. Armature. 



It is a magnet only while the electric cur- 

 rent passes through the wire with which 

 the spools are wound. 



FIG. 143. Illustrating Electrical Induction. 

 .Prim 

 chine. 



A. Prime Conductor of an Electrical Ma- 



fox 

 Mr 



B, C. Cylinder jointed in the middle and 

 insulated on glass legs. 



as in the case of the armature of a horseshoe magnet, the positive pole 

 will be at the negative end of the magnet. This action of a magnet in 

 establishing polarity in a separate body is called induction. Induction 

 takes place whenever an electrified body is brought near a neutral one 

 and is the preliminary part of attraction. If the prime conductor of an 

 electrical machine be brought near a metallic cylinder insulated as in fig. 

 143, the cylinder is instantly rendered polar, the negative tension being 



FIG. 144. 



FIG, 144. Induction by a Battery and Current. 



a. Battery. c. Secondary Coil or Conductor, 



b. Induction or Primary Coil. d. Galvanometer. 



in the end next the positive pole of the machine, and the positive tension 

 at the further extremity of the cylinder. If the positive end of the cyl- 

 inder C be drawn away from the other it will be found to represent a 

 position of potential energy in which the electricity being positive tends 

 to run down to the level of that of the earth. 



