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INVENTIONS OB 1 NIKOLA TESLA.

rangeinent shown in Fig. 236 lias the advantages that the mag-net and armature are kept cool and the strength of the per-manent magnet is better preserved, as the magnetic circuit isconstantly closed.

In the plan view, Fig. 238, is shown a permanent magnet andkeeper plate, t, similar to those in Figs. 236 and 237, with theburners h for the gas beneath the same; but the armature ispivoted at one end to one pole of the magnet and the other endswings toward and from the other pole of the magnet. The springw acts against a lever arm that projects from the armature, andthe supply of heat has to be partly cut off by a connection to theswinging armature, so as to lessen the heat acting upon the keeperplate when the armature a has been attracted.

Fig. 241.

Fig. 240.

Fig. 239 is similar to Fig. 238, except that the keeper t is notmade use of and the armature itself swings into and out of therange of the intense action of the heat from the burner n. Fig.240 is a diagram similar to Fig. 231, except that in place of using aspring and stops, the armature is shown as connected by a link,to the crank of a fly-wheel, so that the fly-wheel will he revolvedas rapidly as the armature can be heated and cooled to thenecessary extent. A spring may be used in addition, as in Fig.231. In Fig. 241 the armatures a a are connected by a link, sothat one will be heating while the other is cooling, and the attrac-tion exerted to move the cooled armature is availed of to drawawav the heated armature instead of using a spring.