Much interest has been awakened among architects. builders and property owners by a new method of increasing natural light in poorly lighted rooms now being introduced by the Luxfer Prism Company, The Rookery, Chicago. The company have established exhibits of their devices at 170 Lake street Chicago; 24 Beekman street New York, and 58 Yonge street, Toronto, Canada. In all these exhibits light is thrown from the ordinary street windows into the darkest recesses of the interior of a deep storeroom and into the basement. The Chicago storeroom is 150 feet deep, and with ordinary glass in the windows it is necessary to provide artificial light to enable the center to be used. But with a frame fitted with Luxfer prisms placed across the upper part of the windows a flood of daylight is poured in so that no artificial light is needed. The effect in the basement is still more marked. The facilities for admitting daylight are very limited,

consisting of the ordinary sidewalk or vault bull's eyes, which merely throw a little light downward and a short distance inward. With the Luxfer prisms arranged below the sidewalk the interior is illuminated so well that a newspaper can easily be read 75 feet from the front.

Luxfer prisms, as illustrated in Fig. 1, are composed of plates of glass with semi-prisms comprising one face. The plates are electrically glazed together into whatever form or size may be required, and are then surrounded with a suitable metal frame. The completed frame of prism plates may be either hung in the window frame or inserted in the sash in place of the ordinary glass. The construction of the prisms has been materially assisted by the application of the Winslow system of electric glazing. The edges of the plates are so welded together by a narrow line of copper that the finished plate is not only attractive in appearance but has also the desired stiffness for use in even very large frames. The form of prisms shown in Fig. 1 is that adapted to diffusing light from ordinary vertical windows. A section of the frame of such plates is shown in Fig 2.

A different application is made in the case of utilizing sidewalk light for the interior of a basement. Fig. 3 shows a prism plate as arranged for this purpose. It would be impossible with a single refraction to carry the light through an angle of almost 90 degrees as would be necessary in this case, and therefore the light is made to pass through two sets of prisms. It is first admitted through a set of heavy glass prism plates set in the sidewalk in the ordinary fashion. This refraction gives the light a backward slant of about 45 or 50 degrees.

The light so refracted is then caught on a frame of prisms hung at the back edge of the sidewalk in a vertical position. Here it is again refracted and the light is carried into the furthest corners of the room as in the case of the Chicago exhibit, 150 feet deep and less than 15 feet wide. The vertical screen of prisms is hung on hinges and when it is raised the rear part of the basement grows dark as though a heavy shutter had been closed. The accompanying cuts, Figs. 3 and 4, perfectly represent the effect of the use and non-use of the prisms in the basement of the Chicago exhibit.

The originator of the idea of lighting interiors by the use of prism plates instead of artificial light is James G. Pennycuick of Toronto, Canada. He interested Chicago capitalists in his invention, who formed the Luxfer Prism Company, to make the necessary commercial arrangements. They secured control not only of the patents covering then use of prisms for lighting purposes, but also patents for electric glazing.

A scientific department was at once established as one of the most important branches of the new company. Prof. O. H. Basquin, who until January 1 was professor of physics at Northwestern University, was employed as the head of this department. It has been the work of this department to improve upon the scientific product made by Mr. Pennycuick by applying to the problem expert

knowledge of the laws of optics by testing the respective refractive powers of various kinds of glass and by studying to ascertain the most advantageous methods of applying the new lighting systems to various buildings.

Each building presents a distinct problem to the scientific department The angle at which natural light strikes a window on the outside, depending on the width of the street, the height of buildings opposite, the point of the compass toward which the building faces, and other conditions peculiar to that building—all these things determine just what sort of prisms are needed and in what position they must be placed to throw the light where it is wanted.

The advantages of the new system are not limited to the mere possibility of giving the light a horizontal direction and thus carrying it further into the building. By using different forms of prisms in different parts of a window all the light striking it may be sent to any part of the room where it is desired.

Architects talk well of the merits of his new device to utilize daylight. They say that it will not only modify new construction, by changing the treatment of light shafts, but it will enable numerous old buildings, almost untenantable for lack of light to be made desirable. In cities particularly the advantages of the prisms are evidently destined to be appreciated.