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FOR MANAGERS AND OPERATORS 133
light rays will have approximately the same area as that of a single human hair.
Beginning with a fact with which all are more or less familiar, viz.: that from each point in a light source rays radiate in all directions (in the case of a projection arc light crater it would not be literally in "all directions," but in all directions over an area covering what would be practically equal to one-half the surface of a globe) until they meet with some obstruction. After leaving the crater the first obstruction encountered is the condensing lens through which the rays must pass. This gives us countless numbers of cones of light as A-l-2, B-l-2, C-l-2, Plate 14, each cone having its apex at a point in the crater, and its base on the surface of the condensing lens. The sum of these cones represents the total light passing through the condenser. Each one of these cones is made up of diverging rays exclusively, up to the rear surface of the condensing lens. With; this I believe we all will agree, and thus endeth the first part.
But when we come to examine into their action beyond the rear surface of the condensing lens we find that the foregoing does not fully elucidate or make clear the entire problem.
First: From each point on the crater we have rays entering every minute pinpoint on the surface of the condenser, therefore through each point of the condenser we have passing a cone of converging rays, each cone carrying a complete image of the crater, as per A-C-2, A-C-1, so that we are also entirely correct when we consider the total light passing from the crater through the condenser as consisting of countless numbers of cones of converging rays having their apex at a point on the condenser at 1-2, Plate 14. It will thus be seen that while we do not actually have two sets of rays we do have a double light action. It may very reasonably be asked: "If the first part includes the total rays passing from the crater through the condenser, and the second part merely does the same thing in a different way, why bother with the second part at! all when the action first described is more generally understood?"
The reason for analyzing the action of light rays completely and describing the second part is because it gives us a clearer understanding of what follows.
Now having in mind one of the cones A-C-1, or A-C-2, Plate 14, it will be readily seen that rays A-l and C-l meeting at a point on the condenser will, even though refracted,