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Patents: 344 of 530	UNITED STATES PATENT OFFICE. OLIN H. BASQUIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE LUXFER PRISM PATENTS COMPANY, OF SAME PLACE.	Olin H. Basquin 18 of 28
PRISM-LIGHT. SPECIFICATION forming part of Letter Patent No. 586,219, dated July 13, 1897. Application filed March 23, 1897. Serial No. 628,842. (No model.)

To all whom it may concern:     Be it known that I, OLIN H. BASQUIN, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Prism-Lights, of which the following is a specification.     My invention relates to prism-lights such as are intended to be afterward assembled in a series to form a prism-plate. Many of these prism lights and plates are adapted to be used either as reflectors or refractors; but in some cases they are desired for refracting only, and there are other reasons for departing from the usual forms of such prism-lights, as will be hereinafter explained.     My invention is illustrated in the accompanying drawings, wherein—     Figure 1 is a plan view of my improved prism-light. Fig. 2 is a section therethrough on line a a. Fig. 3 is an enlarged detail section to illustrate more fully the action of the prism-light on the rays of light which fall upon it. The latter figure also illustrates the distinction between the present invention and previous forms of prism-lights.     Like parts are indicated by the same letter in all the figures.     A is the body of the prism-plates; B B, the primary prisms thereon; C C, the secondary prisms formed on one face of the primary prisms. These primary prisms have each two faces— one, the face D, which is substantially a plane surface, and the other the face which is broken up by the secondary prisms. Each secondary prism has two faces— one, the face E, parallel with the face D, and the other, the face F, which is approximately at right angles to the plane surface C of the prism-light or parallel to the line of vision— that is, parallel to the direction which the light is to take from the prism-light to the point where the illuminating effect is to be secured. This ordinarily is a line approximately at right angles to the receiving-surface of the prism-light.     Referring now to Fig. 3, H H' illustrate what I describe as "low" rays of light striking upon the surface G. J and J', I describe as "high" rays. The ray H, striking the surface at the point H², is deflected to the direction

H³ and emerges from the surface D, taking the direction H4, which is the desired direction, the parts being drawn accurately. It is obvious that this ray therefore emerges from that part of the prism beyond the dotted line H5, and therefore it is obvious that if the part of the prism beyond the dotted line H5 were removed such rays of light would not be properly refracted to reach the part of the room desired to be illuminated. Taking now the ray J, or the high ray, we find that it strikes the surface G at J², whence it proceeds in the direction J³, being refracted at J4 to the direction J5, whence it is in part refracted into the direction J6 and is partly refracted into the direction J7 and refracted at J8 into the direction J9. The lines on the drawings indicating the course of the rays of light are not intended to be precisely exact in position, but are simply designed to diagrammatically illustrate what it is intended to convey. These several parts, so to speak, of such ray are lost for the practical purposes of this prism-light. The last preceding attempts to trace the ray or its part, so to speak, is simply designed to illustrate the fact that the best results may be obtained with reference to high rays, such as the rays J and J', when the part of the prism beyond the dotted line H5 is removed. We are therefore confronted with conditions which are antagonistic to each other, some rays calling for the removal of this portion of the prism and others calling for its retention. Under the ordinary conditions of prism-lights it is found best, if not indeed essential, to keep the surface K at a practically right angle, or, in other words, practically parallel with the line of vision, the surface K having a certain elasticity, so to speak, or descending to a certain degree below the exact right angle to what in this art is known as a "practical" right angle. Now by considering the corresponding low and high rays H' J' we find that by means of the secondary prisms, arranged as shown, the ray H', and of course all other such rays, will be directed into substantially horizontal lines, while the very high rays J' will be directed into the room to be lighted and will not be to any great degree lost. We can therefore secure in a great measure the good results flowing