. Röntgen rays and electro-therapeutics : with chapters on radium and phototherapy . ed in a subsequent chapter. It is necessary by this method tooffer a resistance to the current, owing to the circumstance that thedegree of voltage is too great for the accumulator. The means employedto effect resistance to this excess of current are either a group of lamps orthe rheostat. In the latter method the ammeter is placed in the path ofthe current, and the rheostat is so regulated that the exact voltage sentto the accumulator can be determined by the amperage recorded by theammeter. (Fig. 6.) The sim
. Röntgen rays and electro-therapeutics : with chapters on radium and phototherapy . ed in a subsequent chapter. It is necessary by this method tooffer a resistance to the current, owing to the circumstance that thedegree of voltage is too great for the accumulator. The means employedto effect resistance to this excess of current are either a group of lamps orthe rheostat. In the latter method the ammeter is placed in the path ofthe current, and the rheostat is so regulated that the exact voltage sentto the accumulator can be determined by the amperage recorded by theammeter. (Fig. 6.) The simpler and cheaper method is that obtained by the group oflamps, mounted on a base and connected in parallel. Each lamp (16candle-power) is equivalent to one-half an ampere ; therefore, by thismethod we can accurately estimate the resistance required, by introduc-ing that number of lamps which will be necessary to produce the properamperage for charging the accumulator. When the accumulator is notproperly connected, the lamps burn more brightly than usual. (Pig. 7.) + () (>- i a. -JfJilf-iiU-ALU-U, T — +— + — + — Fig. 7.—Diagrammatic view, illustrating the charging of a battery by a bank of lamps. (3) The alternating current presents the disadvantage that, notbeing unidirectional in character, it requires the employment of aconverter in order to produce a unidirectional current, and also toprovide a low voltage that may be suitable for charging an accumulator. ELECTEICITY AND MAGNETISM. 17 (4) Where it is impossible to obtain a current, as on the battle-field,ingenious use has been made of the bicycle, by employing it as a motoranfl attaching it to a dynamo, which generates the current for chargingthe accumulator. This clever thought originated with Major Battersbyin his memorable Soudan campaign, and the method has been success-fully imitated in South Africa. Other means, but not so practical, areby water-power, windmill, or by horse- or man-power. (5) The fif
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