. American telephone practice . is and other heat coils is usually of such alloy as to melt atabout 1600 F. All of the heat coils mentioned are subject to one objection,which, however, has been brought to notice only in view of an in- 610 AMERICAN TELEPHONE PRACTICE. genious improvement recently made. This objection is that whenonce used it was necessary to throw the coil away or to go to someexpense to put it in proper condition to be used again. In Fig. 444 are shown three views of a type of coil embodyingthis improvement. This is manufactured by the American ElectricFuse Company, of Chicago
. American telephone practice . is and other heat coils is usually of such alloy as to melt atabout 1600 F. All of the heat coils mentioned are subject to one objection,which, however, has been brought to notice only in view of an in- 610 AMERICAN TELEPHONE PRACTICE. genious improvement recently made. This objection is that whenonce used it was necessary to throw the coil away or to go to someexpense to put it in proper condition to be used again. In Fig. 444 are shown three views of a type of coil embodyingthis improvement. This is manufactured by the American ElectricFuse Company, of Chicago, and was designed by Mr. C. A. Rolfe,of that company. In this, the movable part, instead of entirelyseparating from the body of the coil when the solder melts, is merelymoved from one position to another, and in so moving releases thespring which grounds the line. As soon as the spring has been soreleased the circuit through the coil is broken and the parts imme-diately begin to cool. The movable part as soon as sufficiently 1. FIG. 445.—ROLFE ARRESTER. cooled is thus automatically resoldered into its new position inwhich it is, by its other end, again adapted to hold the spring asbefore. Referring particularly to Fig. 444, the only movable part of thisdevice is a small lever shown at the right-hand end of the it is in the position shown in the upper left-hand view of thiscut, the spring of the arrester holder is adapted to be caught underthe lower leg of this lever and thus retained in place. When thesolder holding this lever in this position is softened the spring forcesthe lever into the position shown in the upper right-hand view ofthis cut and the spring is thus released. After the coil is cooled it PROTECTIVE DEVICES. 611 is only necessary to turn it around in the holder in order to bringthe other end of the lever in connection with the spring, as that endis now in such position as to retain the spring. This device may beoperated many hundreds of times withou
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