[Illustration: _=Fig. 13=_] All of the railway motors considered thus far have been of the continuous-current type, although the current to operate them is often obtained from alternating current transmission-systems, through rotary converters, as described above. The alternating current is also beginning to be employed to drive cars and trains. One type of alternating current railway motor, designed for “single-phase” operation, is in use on several interurban systems in this country, running on high-voltage alternating current most of the time, but on continuous current when within the city limits. Other Forms of Electric Traction Electric traction also includes electric automobiles, supplied by storage-batteries; a slow-speed electric locomotive for drawing canal-boats, and called “the electric mule”; and an ingenious gasolene-electric outfit for driving cars by electric motors without any trolley, third rail, or storage-battery. The last-mentioned arrangement consists of a set of electric car-motors mounted on the trucks in the usual way, but supplied with current by a dynamo mounted on the car itself and driven by a gasolene-engine. Thus the car carries its own power-station about with it, and is independent of any outside source of electricity. * * * * * The old alchemists sought to transmute _matter_ from one form to another; and especially lead and other “base metals” into gold, in order that they might grow rich by concentrating the precious metal in their own selfish hands. The modern miracle that electricity works for us, the transmutation of _energy_, is a higher and broader thing, because it multiplies and distributes the world’s good things. APPENDIX A DICTIONARY OF ELECTRICAL TERMS AND PHRASES Everybody is interested in electricity, but the ordinary reader, and particularly the boy who attempts to use this manual intelligently, will come across many technical words and terms that require explanation. It would be impossible to incorporate all needful definitions in the text proper, and the reader is therefore referred to the technical dictionary on the succeeding pages. Care has been taken in its compilation to make the definitions complete, simple, and concise. Some of the more advanced technical terms have been purposely omitted as not necessary in a book dealing with elementary principles. The student in the higher branches of the science will consult, of course, the more advanced text-books. But for our practical purposes this elementary dictionary should answer every requirement. To read it over is an education in itself, and the young experimenter in electrical science should always refer to it when he comes across a word or phrase that he does not fully understand. A =A.= An abbreviation for the word anode.