. Radiotherapy and phototherapy : including radium and high-frequency currents, their medical and surgical applications in diagnosis and treatment ; for students and practitioners . resistance which is opposed to thepassage of the current through the tube and the penetratingvalue of the rays produced. This point has been presentedin a variety of ways in various portions of this work, butit is of sufficient importance to bear repetition. EXACT MEASURES OF DOSAGE 379 To measure and note this resistance at a given sittingso it can be utilized in another, by regulating the tube^Beclere devised an
. Radiotherapy and phototherapy : including radium and high-frequency currents, their medical and surgical applications in diagnosis and treatment ; for students and practitioners . resistance which is opposed to thepassage of the current through the tube and the penetratingvalue of the rays produced. This point has been presentedin a variety of ways in various portions of this work, butit is of sufficient importance to bear repetition. EXACT MEASURES OF DOSAGE 379 To measure and note this resistance at a given sittingso it can be utilized in another, by regulating the tube^Beclere devised an instrument based on the fact that whenin action the spark which fills the air gap between the twopoles at the precise moment the body of air which separatesthese poles ceases to oppose to the passage of the electricitya resistance greater than that existing at the moment inthe interior of the bulb. This is a short circuit and followsthe well-known law that electricity will flow in the path ofleast resistance. The instrument devised to measure thisspark equivalent to the resistance consists of a long metallicrod marked off in centimetres and half-centimetres, ending Fig. Bed eres spintherometer. in a metallic ball at one extremity and having at the otheran ebonite handle. This rod moves through a groovemounted on an isolated upright. The second ball is fast-ened to another isolated upright at about 25 cm. sliding bar and the fixed ball are placed in circuit byattaching each to the respective poles of the static or coilon the one side and with the poles of the bulb on the starting the current the bar is drawn out until the sparkno longer jumps the air space between the bulb, when thedistance in centimetres can be read from the marked rod. 380 RADIOTHERAPY If it indicates too great or too little resistance in the tube,it can be lowered or raised to meet the requirements if thetube is, as it should be, one susceptible of regulation. Thishas the disadvanta
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