. The Röntgen rays in medical work . as become too high. An easy method of temporarily lowering atube is to warm it all over with a spirit-lamp flame or before a warming the tube when it is in action, the operator should 14 THE RONTGEN RAYS IN MEDICAL WORK employ a lamp with a long non-conducting handle to protect him-self from shock and his hands from risk of x-ray burns. A tube whoseresistance is lowered in this way becomes as hard as before as soonas it has cooled ; but prolonged warming of a tube—as, for instanceby baking it in an oven at a high temperature for some hours—willofte
. The Röntgen rays in medical work . as become too high. An easy method of temporarily lowering atube is to warm it all over with a spirit-lamp flame or before a warming the tube when it is in action, the operator should 14 THE RONTGEN RAYS IN MEDICAL WORK employ a lamp with a long non-conducting handle to protect him-self from shock and his hands from risk of x-ray burns. A tube whoseresistance is lowered in this way becomes as hard as before as soonas it has cooled ; but prolonged warming of a tube—as, for instanceby baking it in an oven at a high temperature for some hours—willoften lower an sc-ray tube more or less permanently. Anothermethod of lowering the resistance of a tube which is too highdepends upon the inclusion in a side-tube of a chemical compoundwhich gives off vapour when warmed. When such a tube becomestoo high its vacuum can be lowered by the warmth of a spirit-lampapplied cautiously to the part containing the chemical simple method which may be used to lower the resistance of a. Fig. 4.—Self-regitlatixg Tube (H. Cox). high tube is the following : A sheath of damp lint or cotton-wool isapplied to the kathodal end of the tube. It should extend alongthe glass to a point level with the surface of the kathode, andshould also touch the leading-in wire. It gives a negative charge tothe outside of the glass, and probably promotes the movement ofpositive ions to the region round the kathode. The effect of thisdevice upon the apparent resistance of the tube is very marked,and its use will often permit of the employment of a tube whichotherwise would be too hard for use. Most modern tubes are provided with regulating devices of amore permanent character. One of these methods of tube-regula-tion is the use of an accessory side-bulb to the tube, which isfurnished with terminals between which sparks can be passed at THE ELECTRICAL APPARATUS 15 will. The special terminals of the side-tube are constructed ofsome material which will emi
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