. Dental electro-therapeutics. 0 To determine the proper direction of the rays, the standis of great importance. In the writers opinion, the Lam-bertz stand modified by Dieck, is the most efficient. The horizontal tube-holder can be easily raised or low-ered on the perpendicular shaft, and by means of a secondhorizontal shaft regulated by a cog-wheel it can be length-ened and shortened. A ball-and-socket joint at the end ofthe horizontal arm permits the turning of the tube-box inevery direction, and of its easy adjustment. Lately thewhole end-joint of the arm has been made to turn aroundthe pe
. Dental electro-therapeutics. 0 To determine the proper direction of the rays, the standis of great importance. In the writers opinion, the Lam-bertz stand modified by Dieck, is the most efficient. The horizontal tube-holder can be easily raised or low-ered on the perpendicular shaft, and by means of a secondhorizontal shaft regulated by a cog-wheel it can be length-ened and shortened. A ball-and-socket joint at the end ofthe horizontal arm permits the turning of the tube-box inevery direction, and of its easy adjustment. Lately thewhole end-joint of the arm has been made to turn aroundthe perpendicular axis, which facilitates still further thefixing of the tube at the required angle. The centralizingtelescope which is attached to a hinge and pushed aside 170 ELEC TRO-PH YSICS before the current is turned on, is a valuable device, whichpermits of the most accurate adjustment; it can also be usedas a visor for determining the centre of the target. Toinsure absolute correctness of focus the current should be Fig. 75. The Lambertz stand. THE X-RAYS OR RONTGEN RAYS 171 turned on and the rays allowed to pass through the tube, asmall and perfect luminous disk should appear on the fluor-escent screen. The cylinder of x-ray-proof material, providedwith an adjustable diagram, cuts out the secondary rayswhich do so much to impair the sharpness of the radio-graph, and of which more will be said later. When the operator is in a position to direct the rays in astraight line through the middle of the cylinder, the nextquestion he must consider is the relation of this line; firstly,to the axis of the tooth or root, and, secondly, to the planeof the film or plate; and here he must observe certain prin-ciples of projection which in themselves are simple, butwhich it may be well to recall. Fig. 76 Fig.
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