170 



GENERAL SCIENCE 



is rubbed with dry silk. In the apparatus case of the physics 

 room there was likely to be a static machine with various 

 pieces of apparatus to use with the machine. Interesting 

 as these experiments were, and valuable as the instruction 

 accompanying them may have been, they receive far less 

 attention now. 



The study of the flow of an electrified condition along 

 conductors (wires) as current electricity, and the mainte- 

 nance of this electrified condition by means of cells and batter- 

 ies of various kinds, is still an important part of courses in 



high school physics. But more 

 and more time is being given to 

 the study of electrical currents, 

 electrical devices, and electrical 

 changes in those cases where the 

 electricity is produced by dynamos. 

 The problem of transmission of 

 electrical energy without wires 

 has been solved. But other achieve- 

 ments and further advances in 

 human knowledge concerning 

 electricity are probable. Even sluggish minds may well 

 be stimulated in efforts to master what has already been 

 accomplished in order to be prepared to comprehend and 

 to make use of what is yet to be learned and applied. 



The production of electrical energy is closely associated 

 with magnetism in the dynamo, and with chemical changes 

 in cells. The existence of electricity in a circuit produces 

 magnetic, chemical, and heating effects. These may be 

 seen, for example, in the electromagnet, the electric lamp, and 

 in electroplating. An excellent illustration is afforded in 

 these relationships of the significance of the phrase " correla- 

 tion of forces" such a relationship that through the action 

 of one force another force manifests itself. 



FIG. 57. An electromagnet. 



