THERMO-MAGNETISM AND PTllO-MAGNETISM.

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Mr. Tesla has also devoted his attention to the development ofa pyromagnetic generator of electricity 1 based upon the following-laws : First, that electricity or electrical energy is developed inany conducting body by subjecting such body to a varying mag-netic influence ; and second, that the magnetic properties of ironor other magnetic substance may be partially or entirely destroyedor caused to disappear by raising it to a certain temperature, butrestored and caused to reappear by again lowering its tempera-ture to a certain degree. These laws may be applied in the pro-duction of electrical currents in many ways, the principle ofwhich is in all cases the same, viz., to subject a conductor to avarying magnetic influence, producing such variations by the ap-plication of heat, or, more strictly speaking, by the application oraction of a varying temperature upon the source of the magnet-ism. This principle of operation may be illustrated by a simpleexperiment: Place end to end, and preferably in actual contact,a permanently magnetized steel bar and a strip or bar of soft iron.Around the end of the iron bar or plate wind a coil of insulated wire.Then apply to the iron between the coil and the steel bar a flameor other source of heat which will be capable of raising that por-tion of the iron to an orange red, or a temperature of about 600°centigrade. When this condition is reached, the iron somewhatsuddenly loses its magnetic properties, if it be very thin, and thesame effect is produced as though the iron had been moved awayfrom the magnet or the heated section had been removed. Thischange of position, however, is accompanied by a shifting of themagnetic lines, or, in other words, by a variation in the magneticinfluence to which the coil is exposed, and a current in the coilis the result. Then remove the flame or in any other way reducethe temperature of the iron. The lowering of its temperature isaccompanied by a return of its magnetic properties, and anotherchange of magnetic conditions occurs, accompanied by a currentin an opposite direction in the coil. The same operation may be

1. The chief point to be noted is that Mr. Tesla attacked this problem in away which was, from the standpoint of theory, and that of an engineer, farbetter than that from which some earlier trials in this direction started. Theenlargement of these ideas will be found in Mr. Tesla’s work on the pyromag-netic generator, treated in this chapter. The chief effort of the inventor wasto economize the heat, which was accomplished by inclosing the iron in a sourceof heat well insulated, and by cooling the iron by means of steam, utilizing thesteam over again. The construction also permits of more rapid magneticchanges per unit of time, meaning larger output.