. The Röntgen rays in medical work . charge from the mains with a lamp in series, the batterymust be connected so that the current which goes through it mustalso go through the lamp. In the case of a lamp suspended by aflexible wire the conditions would be met by cutting one of the twostrands of the double wire, and untwisting the cut ends for a fewinches, so as to give sufficient length for connection to the two ends THE ELECTRICAL APPARATUS 57 of the battery. As one of the severed ends is positive and theother is negative, there will be a right and a wrong way of con-necting up. In the forme
. The Röntgen rays in medical work . charge from the mains with a lamp in series, the batterymust be connected so that the current which goes through it mustalso go through the lamp. In the case of a lamp suspended by aflexible wire the conditions would be met by cutting one of the twostrands of the double wire, and untwisting the cut ends for a fewinches, so as to give sufficient length for connection to the two ends THE ELECTRICAL APPARATUS 57 of the battery. As one of the severed ends is positive and theother is negative, there will be a right and a wrong way of con-necting up. In the former the direction of the current from themain will be opposed to that of the battery, the lamp will burnmore dimly, and the battery will receive a charge. In the latter itwill not receive a charge, but, on the contrary, it will discharge,reinforcing the current of the main, and the lamp in the circuit willburn too brightly. The effect on the lamp is the simplest guide tothe right way of connecting in the battery, and when once deter-. Fig. 31.—Charging through a Lamp-Resistance (Biggs and Co.). mined the ends may be marked in some way for future way of testing the polarity of the ends of wire is to uselitmus-paper; the paper will be reddened where it touches thepositive pole, and turn blue where it touches the negative. If, instead of considering a flexible wire divided as just described,we consider a piece of electric light wiring enclosed in the ordinarywood casing, it will be seen that the same results can be obtainedby removing a few inches of the casing cover ; one of the two wirescan then be cut, and the ends bent up a few inches apart, and 58 THE RONTGEN RA YS IN MEDICAL WORK brought through holes in the cover, where they may be attachedto binding screws for the sake of neatness. The battery can thenbe attached to these binding screws by means of wires when it iswished to charge, and when charging is not in progress the batterycan be detached and remove
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