We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
364 RICHARDSON'S BLUEBOOK OF PROJECTION
The carbon rod surrounding the core (where there is a core) provides most of the crater floor area. The core serves several purposes as already indicated but in addition the various chemical elements with which it is impregnated make it either a high or low intensity carbon, or any one of several other sorts, including White Flame and a.c. carbons.
(22) The source of the most intense light varies in different types of arcs. There are three general types. In the low intensity arc (which is essentially obsolete but still has not been replaced in many theatres) the crater of the positive carbon is the light source ; the carbon there being at or near the point of volatilizing into gas. In the so-called flame arc, the arc itself, made more luminescent by the inclusion of rare earth materials in the carbon core, is the essential source of light, the incandescence of the carbons being unimportant in comparison. In the high intensity arc, the combination of rare earths in the carbon core and a greater current density (more amperes in proportion to crater diameter) creates a relatively deep crater; the floor of this crater contains a concentration of rare earth materials that have been volatilized and are in gaseous form; these concentrated gases, plus the crater surface itself, are the principal sources of high intensity light.
(23) It is essential to good results that the entire area of the crater floor have, as nearly as possible, an even temperature, which gives a uniform luminosity. This can be accomplished only by the use of very pure carbon materials. Should impurity occur at any point, or carbon density vary at different points of the crater floor, there will be a variation in the resistance to the current; as a result current flow and luminosity will not remain constant until the fault, whatever it be, has burned away. This being self evident, we may readily understand the importance of pure materials and of good mixture to provide uniform density of the carbons at every point.
With high intensity the source of light, as said, is very largely the highly luminous gas or vapor contained in the