File:Light energy, its physics, physiological action and therapeutic applications (1904) (14777941193).jpg

Identifier: lightenergyitsph00clea (find matches)
Title: Light energy, its physics, physiological action and therapeutic applications
Year: 1904 (1900s)
Authors: Cleaves, Margaret Abigail, 1848-1917
Subjects: Medicine, Physical Phototherapy Light Radioactivity
Publisher: New York, Rebman company (etc., etc.)
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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and the amount of current consumed. The tem-perature of the negative carbon is between 2,ioo°C. or3,772°F. and 2,500°C. or 4,532°F. This tremendous tem-perature of the electric arc renders it very efficient in electricwelding and in operating electric furnaces. Both tempera-ture and luminosity are chiefly due to the conversion of elec-tric energy into heat, but are partly derived from combustionof the carbon in air. The dazzling brightness of a carbon arc, a miniaturesun in fact, is such that it can only be observed throughsmoked or densely colored glass. Upon examination inthis way, the observer notes that the arc or bow-shapedbluish flame which appears in the gap between the two op-posed carbons is very much less brilliant than the ends ofthe carbons themselves. The characteristic change in theshape of the arc will be noticed after it has been maintainedfor a short time, i.e., the end of the positive electrode is hol-lowed out in the form of a small crater, while the negative f
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Fig. i.—Carbons used in clinical work with a 25-ampere arc.The upper or positive carbon shows the crater-like depression, thelower or negative carbon the nipple-like projection. The area of in-candescence is clearly shown as well as the disintegrating actionupon the carbons under the double influence of volatilization andoxidation. THE PHYSICS OF LIGHT ENERGY. 89 or opposed carbon has a minute nipple-like projection formedon the end just opposite the crater in the positive carbon.The positive carbon is brighter than the negative, but mosl of the light, however, issues from the crater itself. Asthe power of any body to emit light increases with itstemperature, an inspection of the arc quickly confirms thestatement made that the crater is the hottest part of thearc. With the current strength ordinarily employed, the in-candescence of the carbons extends to but a comparativelyshort distance from the tips. This is the region in whichthe burning of the carbons or the oxidation is most ma

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