. Dental electro-therapeutics. Wire resistance. A convenient and effective rheostat for a battery, whereno current collector is attached or necessary, consists ofa slate core around which is wound many hundred turnsof insulated wire, a sliding metallic contact spring is ad-justed to move over the coils of wire, making contact withportions of the wire from which the insulation has beenremoved, in such a manner that contact with each turn ofthe wire decreases the resistance by the amount of resistancein the length of wire that passes around the slate core,which, in this instance, is about vo
. Dental electro-therapeutics. Wire resistance. A convenient and effective rheostat for a battery, whereno current collector is attached or necessary, consists ofa slate core around which is wound many hundred turnsof insulated wire, a sliding metallic contact spring is ad-justed to move over the coils of wire, making contact withportions of the wire from which the insulation has beenremoved, in such a manner that contact with each turn ofthe wire decreases the resistance by the amount of resistancein the length of wire that passes around the slate core,which, in this instance, is about volt, and the currentstrength is very gradually increased. This form of rheo-stat is largely used on switchboards to reduce the currentfrom the main. It requires careful attention in a dampclimate, for, should the wire oxidize, the insulation is liableto become imperfect, and the current brought on in irregular 118 ELECTRO-PHYSICS. jerks which is uncomfortable to the patients. Should thisoccur the instrument should be discarded. Current Reverser or Commutator.—This is a useful additionto the equipment of a battery for dental purposes, althoughnot so essential as for medical workFig. 49 in examining muscle and nerve re- actions. It is a convenience, insteadof changing the wires, to be able toreverse the poles of the battery bysimply moving a pair of crank armsto an adjoining stud to which thereverse wires are connected insidethe battery. In ionization, some ionsare obtained at the negative pole(iodine for example) in using thecurrent, when the reverse to theusual current is desired, simply mov-ement reverser. ing the crank arm, Fig. 49, bringsabout the desired or Conducting Cords.—Rheophores or con-ducting cords are made of insulated flexible wire finishedoff at each end with suitable metallic connecting ends forattachment to the terminals of the battery and should be of suff
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