US2432867A - Polarizer and polarizing lamp - Google Patents

Description

Dec. 16, 1947. J. F. DREYER POLARIZER-AND POLARIZING LAMB Filed Aug. 21, 1941 3 Sheets-Sheet 1 Dec. 16, 1947. J. F. DREYER POLARIZER AND POLARIZIIiG LAMP Filed Aug. 21, 1941 3 Sheets-Sheet 2 Pk/JMA r/c lava Dec. 16, 1947. J. F. DREYER POLARIZER AND POLARIZING LAMP Filed Au 21, 1941 s Sheets-Sheet 3 fi/RkoR, END.

ffneeoe 46K INVENTOR fix! A" D M ORNEY Patented Dec; 16, 1947 POLARIZER AND POLARIZING LAMP John F. Dreyer,

Cincinnati, Ohio, assignor to The General Polarizng Company,

Cincinnati,

Ohio, a corporation of Ohio 7 Application August 21,, 1941, Serial No. 407,720

This invention relates to a light polarizing device and particularly to lamps adapted to polarize light emitted therefrom.

Prior to my invention much has been done in the study of properties of polarized light, various practical utilizations have been suggested, and in some cases adopted, wherein light from various sources has been polarized by massive crystals, oriented crystalline films, and reflecting plates. So far as I am aware, however, all of such applications have related to the passing of a more or less uni-directional beam of light through, or reflecting upon, a plane surface polarizer, and it has not been found practicable prior to my invention to effect polarization on curved and irregular surfaces and particularly directly upon the surfaces of lamps and lenses.

I have now discovered that this is both possible and feasible and I have disclosed in my co-pending applications Serial Nos. 217,249, 263,779 and 384,550, materials and apparatus particularly adapted for applying a polarizing coating to the surface of lamps, lenses and other curved and non-planar surfaces. My present application is a continuation-in-part of said prior co-pending applications.

Accordingly, it is one object of my invention to provide lamps, lenses and other optical devices of shape determined by their primary uses which are adapted directly to polarized light emanating therefrom or passing therethrough without the necessity for separate polarizing devices.

Another object of my invention is to provide automobile headlamps adapted to reduce or eliminate glare.-

Another object of my invention is to provide lamps for reading, display and other purposes which will avoid glare.

Other objects of my invention will appear from the following description and the accompanying drawings. v

Although in these drawings and in the following specification I have shown a preferred embodiment of my invention and various alternatives and modifications thereof, it is understood that these are not intended to be exhaustive nor limiting of the invention, but, on the contrary, are given with a view to illustrating and explaining the principles of the invention and their embodiment for practical use, in order that others skilled in the art may be enabled to adapt and modify them in numerous embodiments and modifications, each as may be best adapted to the conditions of any particular use.

Figure l is a side elevation of a lamp bulb em- 11 Claims. (Cl. 176-34) bodying my invention with the direction of polarization, i. e., the electric vector of polarized light at each point, lamp surface and a parabolic reflector, lens and housing for the lamp indicated by the broken lines surrounding the lamp;

Figure 2 is a top plan view of the lamp shown in Fig. 1;

Figure Bis an end elevation of that shown in Figs. 1 and 2;

Figures 4, 6, 8, 10, 13, 14 and 15 are views in side elevation of other lamp bulbs embodying my invention;

Figures 5 and '7 are top plan views similar to Fig. 2, but showing other embodiments of my invention; and

Figures 9, 11 and 12 are views in end elevation respectively of the lamp bulbs shown in Figs. 8, 10 and 13.

Referring first to Figs. 1 to 3 inclusive, the lamp In there shown is of standarddesign commonly used in automobile headlights, spotlights and the like. This, as well as the other forms of lamps commonly used and including those illusa lamp such as 5 trated in' the drawings, may be broadly described as pear-shaped, one end I l containing the stem of the lamp and tapering towards the connector base l2, corresponding to the stem end of the pear and, therefore, being referred to herein generally as the stem side or stem end of the lamp and the opposite end l3 of the lamp being, in general, lens-shaped and serving either as a light permeable wall or lens for the emission of direct illumination, or as a concave reflector.

According to the present invention, some or all of the surfaces of these lamps are coated with a light polarizing material. In the preferred embodiment of my invention these materials are plane-polarizers and may be dyes or other materials which are in themselves capable of polarizing light or are capable of being readily converted into pleochroic and especially dichroic materials capable of polarizing light and which exhibit a nematic state. These materials, in the preferred embodiment of my invention, may be applied and oriented in accordance with my invention described and claimed in my copending application, Serial No, 384,550, filed March 21, 1941, which method may be described generally as consisting of rubbing the surface which is to become the polarizing surface uniformly in one direction along the line or lines on which the polarizing material is to be oriented and subsequently applying the polarizing or polarizable material in a film, preferably fused or dissolved,

indicated by broken lines on the tions for after and bringing it into the nematic state wherein it is. oriented along the lines of rubbing by a field efiect resulting from the rubbing. and is then quickly and uniformly solidified from the nematic state so as to set the orientation before any reorientation or other disturbance, e. g., due to crystallization, can occur. I use the term "polarizable herein to include both materials which, when properly oriented, are inherently capable of polarizing light passed therethrough and materials which may be made capable of polarizing light by a subsequent treatment which does not disturb their orientation.

As one example, I may coat automobile headlamps as follows: The surface of the glass first is cleaned, for example, by dipping it in a concentrated solution of 100 parts by weight of potassium bichromate and 70 parts concentrated sulphuric acid 66 Baum. After ten minutes the bulb is removed from the solution and adhering chemical is washed off. The surface is then wiped dry with clean absorbent paper or a cloth, rubbing along th lines of the desired orientation, e. g., as indicate at I5, I etc. on Figs. 1, 2 and 3, or the surface may be dried by evaporation if subsequent rubbing treatment is carried out for orientation; for example, by a bumng wheel, e. g., of cotton or wool cloth, or felt or of paper. The direction of rubbing, or in the case of the bufllng wheel, the plane of the wheel, in this treatment will always be kept parallel to the lines of orientation desired on the finished lamp, e. g., as indicated in Figs. 1 to 3 by the broken lines [5. l5, etc. It is this rubbing in the present example which produces the desired orientation and controls the plane of polarization of the resulting polarizing surface.

To this rubbed surface I now apply a film of the polarizable material which may be, for example, a solution consisting of twenty, parts by weight of methylene blue (zinc free) dye in one hundred parts of methyl alcohol. The film may be applied by dipping the bulb into the solution and removing it,'e. g., at a uniform speed of two inches per minute into an atmosphere saturated with methyl alcohol. When the bulb is completely removed, it is shifted quickly into a gentle current of dry air of relative humidity below 30%, which flows uniformly across its surface. The air temperature may be, for example, between 50 F. and

80 F., and the air speed is preferably regulated so that each point on the film dries in about three seconds after it comes into the dry air stream.

When the coating has dried the bulb is dipped into a solution containing 2% sulphuric acid and saturated with potassium dichromate. The coating is then washed gently with water and dried in air. For further protection of the-film it can be clipped in a 5% solution of methylmethacrylate resin in toluol and again dried. If the lamp is a design which gets very hotduring use, vinyl acetate polymer or sucrose octa-acetate may be included in the dye solution or coated onto the oriented film instead of the methacrylate coating, these latter resins being more resistant to the heat than the methacrylate resin. These solutreatment'of the film are designed to avoid redissolving the methylene blue and do not destroy its orientation.

As an example of a fused coating, a bulb prepared as in Example 1 may, instead of being treated with the methylene blue solution as described above, be dipped into a fused bath of azoxyphenetol, maintained at a temperature of about 134 to170 c. In this case, instead 9? an 4 atmosphere saturated with solvent, I use an atmosphere above the bath kept at a temperature above the upper melting point of the azoxyphenetol. The bulb is withdrawn into this atmosphere as it was withdrawn from the methanol solution in Example 1. When the coating is complete, the bulb temperature is reduced so that the cooling of the film progresses from the interior outward or uniformly throughout and solidification thus takes place uniformly throughout the thickness of the film or progressively from the inside out, but in any case sufllciently fast so that crystallization does not occur. If desired, these operations can be effected by use of an automatic apparatus as set forth, for example, in my prior co-pending application Serial No. 217,249, filed July 2, 1938.

The lamp may be made of clear or diifusing glass ii the polarizing layer is applied to the outer surface. Of course if the polarizing layer is on the inside, the polarized light passing from it should not be subjected to diffuse reflections by particles or bubbles suspended in the glass wall. Also, if the planes of polarization are not parallel for different areas, the mixing of light from such areas by use of diffusing glass will to that extent defeat the usual purposes of polarization.

The orientation along the lines as illustrated in Figs. 1 to 3 inclusive, can be most easily developed by rubbing the bulb on a bufilng wheel, moving the lamp with respect to the wheel so that the point of contact and the plane of the .wheel follow along lines of desired orientation,

e. g., as those shown on the drawings.

The lamp with polarizing surfaces thus oriented is designed to be used in a parabolic metallic reflector such as has commonly been used in the past in automobile headlamps, spotlights, etc. e. g., as indicated in direct illumination coming through the lens end l3 of the bulb I0 is plane polarized with its plane of polarization vertical. (By'plane of polarization in this specification I mean to refer to the plane in which lies the polarized light, and I do not use the phrase "plane of polarization in the obsolete sense, meaning perpendicular to the vector of the polarized light.) This direct illumination. is, therefore, of a type which does not readilyproduce a glare, for example, on wet streets, or by reflection on nonmetallic surfaces, and can be eliminated, if desired, by the use of an analyzer on the windshield or in eye-glasses in an approaching vehicle or pedestrian.

On the stem side ll of the bulb the orientation is such that at the top and the bottom of the bulb the plane of polarization is coincident with the vertical axial plane through the bulb. The light insofar as it passes through the bulb in this plane, will, therefore, be. similarly polarized to that which comes directly through the'lens end l3 of the bulb, but to a large extent this light may be more or less extinguished on the parabolic metal reflecting surface by reason of its plane of polarization coinciding with the plane of incidence on the mirror surface.

At the sides of the lamp the orientation is such that the plane of polarization is substantially perpendicular to the axis of the lamp. This light, therefore, will be reflected from the parabolic mirror surface without reduction of its intensity,-

Between the top and bottom, respectively, and] broken lines in Fig. 1. The

electrical vector of the the sides, respectively, are areas of the bulb in which orientation is such that the plane of polarization will be neither coincident with, nor perpendicular to, the plane of incidence on the reflector, and the light passing through these areas will, therefore, be more or less converted into elliptically or circularly polarized light by reflection from the mirror surface. In this application I shall use the generic term elliptically polarized light to include both elliptical and circular polarization.

The total beam from the lamp and its reflector, therefore, will be composed of a preponderance of light plane-polarized in a vertical plane with progressively smaller amounts of light progressively more elliptically polarized. This is a desirable beam in that it gives an appreciable amount of light from glare surfaces and through analyzers, whereas a major proportion of the light which would otherwise become glare, may be extinguished by reflection from a wet road or by passage through a crossed analyzer. Thus objectionable or blinding glare is eliminated at the same time that the natural appearance of objects, including their specular reflection properties, is retained.

In Figs. 4 and 5, I have shown a lamp of similar design; but in this case the lines of orientation are curved oppositely as will be clearly apparent by comparison with Figs. 1 and 2. Similar results to that described above are obtained with this lamp.

In Figs. 6 and 7, I have shown another type of orientation in which the lamp when treated on the bufiing wheel is kept with the same axial plane thereof always parallel to, and at a fixed space relation to, the plane of the buffing wheel, while the lamp is rotated about a diameter of its great circle perpendicular to said plane. In this case, as in the cases discussed above, the light emitted from the top and bottom of the lamp is plane-polarized with its plane of polarization coincident with its plane of incidence on the parabolic reflector, whereas, the light emitted at the sides is plane-polarized with its plane of polarization perpendicular to the plane of incidence; and, in the areas between, light will be emitted plane-polarized at varying angles to the plane of incidence on the reflector. These three forms of my invention differ principally in the proportion and degree in which light from the intermediate area is elliptically polarized upon reflection.

The lens end l3 of the bulb may, instead of serving as a polarizer, asindicated 'in Fig. 8, be silvered or coated with other reflecting material so that it serves as a concave reflector to throw light from filament or other light source back through the stem side I2 of the lamp. Where the lamps are to be used in reflectors as described above, the effect of this is to increase the proportion of elliptically-polarized light and to reduce the proportion of plane-polarized light in the ultimate beam. By orienting the polarizing film so that the plane of polarization at each point is at an angle, e. g., 45, to the axial plane through that point, as illustrated in Figs. 8 and 9, and using such bulb in a silvered parabolic reflector as shown, the combination is a valuable source of elliptically-polarized light, and the extent that the angle of the orientation and the slope ofthc parabola are chosen to give the critical relation for circular polarization by reflection of planepolarized light, the device will serve as a source of circularly-polarized light. Right or left-hand circular or other elliptical polarization may be polarized in the obtained according to the direction of the spiral lines of orientation. I

I may, on the other hand, silver or otherwise convert the stem side H into reflecting surface so that the light falling on this side from the fila ment or other light source is reflected out through the lens end l3 and thus the entire output of the lamp may be plane-polarized with little or no conversion to elliptically-polarized light. If the stem side II is of parabolic form as shown, for example, in Figs. 10-11, the parallel beam may thus be directly established as a plane-polarized light beam.

In Figs. 12 to 15, I have shown other types of lamps designed for general illumination, and particularly for road lighting, store and display lighting and reading lamps.

In Fig. 13 is shown a lamp of any ordinary design which the polarizing coating is oriented along lines corresponding with the intersection of the bulb surface with the axial planes through the bulb. Advantageously a reflector type lamp may be used, reflector lamps, with the upper half of the bulb silvered to reflect all light downward through the lower half of the bulb, and the lower half of this bulb I have coated with a polarizing material oriented, e. g., in the manner described above. Thus, the electric vector of polarized light emitted from the lamp will, in all cases, be in vertical planes radial to the lamp, with a consequent substantial reduction in the glare from specular reflecting surfaces on which the light falls. This is particularly important for store lighting and for reading. In stores, the goods for sale are often displayed in glass cases and the glare from the general illumination in the room seriously interferes with the view of the goods unless a very much higher intensity of illumination is used within the cases than would otherwise be required. By cutting down the glare from the glass, the internal illumination in the glass cases can be correspondingly cut down with equal effectiveness of display, or the efiectiveness of the display can be increased with equal illumination.

In libraries, studies and other locations where such a lamp is to be used for reading, the glare from smooth pages, and especially from' glazed paper, is greatly reduced by my invention, with consequent reduction of eye strain.

In Fig. 14, I have shown a test tube type lamp designed to be burned in horizontal position; and in this case the polarizing material is oriented in vertical planes as indicated by the lines l5 Onehalf of this lamp may be silvered, as shown, and the other half is provided with a polarizing material oriented on lines indicated. The result of the use of this lamp is substantially the same as the use of a lamp such as that shown in Figures 12 and 13, but with some additional advantages where an analyzer is to be used, particularly in the case of road lighting where automobiles are equipped with horizontally oriented analyzers. If such analyzers are arranged to extinguish light vertical plane, the polarizing material on this lamp would, of course, be oriented as shown, so as to produce vertical plane polarization; whereas, if the analyzer is arranged to extinguish light in a horizontal plane, the polarizing material on the lamp would, of course, be oriented so as to produce plane polarization in horizontal plane; and if the analyzer is arranged for extinction of light polarized in an oblique plane, the polarizing material of the lamp would be oriented so as to produce polarization in such 7 oblique plane, e. g., on a 45 spiral orientation as indicated, for example, by the broken lines l in Figure 15.

It is an advantage of this latter arrangement, as shown in Figure 15, that the planes of orientation of the polarizing material on opposite sides of the lamp are mutually perpendicular whereby the component of light reflected from the polarizing film on one side, since its plane of polarization is perpendicular to the transmitted component, may pass without extinction through the opposite side to which it is reflected. A somewhat similar advantage is obtained with the partially silvered lamp, such for example as those shown in Figures 8 to 14 inclusive, in that the reflected component of the light reflected from the polarizing film will be converted, by reflection at a suitable angle from the silvered portion of the lamp, into elliptically or circularly polarized light, which will then pass through the polarizing portions of the lamp with a re-polarization but without extinction. If instead of a metallic mirror a difiuse reflecting surface is provided above the polarizing lens or window, a similar effect will be attained in that the reflected component will be depolarized by diffuse reflection and will thereupon intensify the unpolarized light from the light source which is incident upon the polarizing lens or window. Likewise, a rotatory plate or \/4 (quarter wave) plate, e. g., of mica, etc., may be used within the lamp to rotat the plane of polarization or to change the plane polarization to circular polarization in the reflected component and thus to allow such light to pass through the polarizing film.

The polarized coating, according to my invention, is applied either on the outside or the inside surfaces of the bulb. In general, it will be found more satisfactory to coat the outside because of the greater ease of the rubbing operation, but it will be understood also that by use of small tools or particularly in the case of preformed lenses, as illustrated in Figure 11, it is not at all impracticable to form the coating suitably oriented on the interior of the bulb, and this affords the advantage that the bulb itself protects the coating.

In the case of scaled beam type headlamps, e. g., as shown in Figures and 11, where the lens end is exposed directly to the weather and abrasion, it is desirable to protect the polarizing film, e. g., in the manner suggested above, by a superficial coating of resin, or by a concaveconvex lens of glass or of premolded resin fitted over the polarizing lens.

I general, my invention includes all kinds of pellucid-transparent and translucentarticles in which at least one principal surface is or includes a compound-curved surface, i. e., one which cannot be generated by movement of any line-straight, curved or jagged in a single direction parallel to a straight line directrix or by any movement of a straight line while kept parallel to a directrix, and on which surface is provided a light-polarizing layer which is oriented along lines similarly related to a common axis, as for example along spiral lines, circular, elliptical, parallel, radial, etc.-or along the intersections ofradial or parallel planes or geometrical surfaces with said polarizing layer, whereby light passing through said layer has a certain uniformity of polarization depending upon the regularity of said orientation.

Th polarizing lamps shown in the accompanying drawings, and as set forth and described in the above specification, represent but one of sev-' eral types of articles in which compound-curved surfaces are made polarizing by the application of non-crystalline films in accordance with my invention. So far as I am aware, my invention provides, for the first time, a simple light-polarizing coating on such compound-curved surfaces, although it has been feasible heretofore in simple curved surfaces, by treating the polarizing film as a fiat film and then fitting it to the surface by simple bending without stretching, to provide an oriented film of suspended crystalline particles.

Another important example of the broad application of 'this invention is in the field of optical lenses for various purposes, including eye-glasses, goggles, binoculars, telescopes, cameras, Windshields, windows, mirrors, light valves and polarizing filters, etc. Where the optical element is made of two transparent parts fitted together, as in the case of lenses corrected for chromatic aberration, shatter-proof glass windows, etc., the polarizing film may be applied to the surface of the glass which is to be covered by the other piece, so that this film is sandwiched between the two pieces of glass and is protected thereby. In the case of accurate lenses, the film will ordinarily be appliedrelatively thin and without other materials, such as resin or other lacquer ingredients. In the case of shatter-proof windows, etc., polarizing material may be incorporated in a lacquer solution or in or upon a resin or c'ellulosic film which may form or become a part of the flexible cementing layer between the two layers of glass; and it is an important advantage of my invention that it is thus possible to include the polarizing material in such standard optical construction,

In my co-pending applications Serial Nos. 394.550. filed March 21, 1941; 263,779, filed March 23, 1939; and 217,249, filed July 2, 1938, I have described and claimed various polarizing films and materials and various methods and apparatus for applying the same.

What I claim as new is:

1. An incandescent lamp comprising, in combination, a filament light source, an envelope therefor a portion at least of which is transparent, at least a portion of said envelope being non-planar, said envelope substantially encompassing said source, a non-planar portion at least of said envelope being coated with a material which polarizes transmitted light, said coating being aflixed to and positioned on said envelope to intercept light beams emanating from said source.

2. An incandescent lamp comprising, in combination, a filament light source, an envelope therefor a portion at least of which is transparent, said envelope substantially encompassing said source, the transparent portion of said envelope being non-planar and being coated with material which polarizes light by transmission thereof, said material being aifixed to said envelope and intercepting beams emanating from said source and traversing the said transparent portion of said envelope.

3. An incandescent lamp comprising, in com bination, a filament light source, an envelope therefor a porti'on at least of which is transparent, said envelope substantially encompassing said source, the transparent portion of said envelope being non-planar and being coated on its outer surface with material which polarizes light by transmission thereof, said material being affixed to said surface and intercepting beams emanating from said source and tranversing the said transparent portion of said envelope.

4. An incandescent electric lamp having the outer non-planar surface of the transparent envelope thereof adhesively coated with a lightpolarizing material which polarizes by transmission light emanating from said lamp.

5. A polarizer comprising an, optical support having an optical surface departing substantially from a geometric plane and an uninterrupted and unstressed substantially permanent coating of a non-crystalline dichroic polarizing material on, and conforming in shape to, said surface, the molecules of said dichroic material. being uniformly oriented along predetermined lines relative to said surface, with adjacent molecules of said material substantially parallel, and uniformly polarizing light incident thereo at all angles thereto, with said polarization uniformly conforming to the pattern of said predetermined lines.

6. A polarizing lamp which comprises aradiant light source, a lamp wall surrounding said light source and comprising a light-permeable fall having an optical surface departing substantially from a geometric plane and an uninterrupted amd unstressed substantially permanent coating of a non-crystalline dichroic polarizing material on, and conforming in shape to, said surface, the molecules of said dichroic material being uniformly oriented along predetermined lines relative to said surface, with adjacent molecules of said material substantially parallel, and uniformly polarizing light at all angles incident thereon from the interior of the lamp, with said polarization uniformly conforming to the pattern of said predetermined lines.

7. A polarizing lamp which comprises a radiant light source, a lamp wall surrounding said light source and adapted to reflect radiation from said source back into the interior of the lamp, at least a part of said wall being of a permanent non-crystalline dichroic polarizing material adapted to separate the ordinary and extraordinary rays, each polarized on an axis transverse to that of the other, and to reflect one of said rays back into the interior of the lamp while transmitting the other, the molecules of said dichroic material being uniformly oriented along predetermined lines relative to the surface of said lamp wall, with adjacent molecules of said material substantially parallel, and uniformly polarizing light at all angles incident thereon from the interior of the lamp with said polarization uniformly conforming to the pattern of said predetermined lines.

8. A polarizing lamp as defined in claim 7 wherein the molecules of the dichroic material are oriented along spiral lines approximately coaxial with the lamp, whereby the polarized component which is reflected into the lamp is polarized on an axis which assures its transmission by the polarizing material at the opposite side of the lamp wall.

9. A polarizing lamp as defined in claim 7 wherein the molecules of the'dichroic material are oriented along spiral lines coaxial with the 10 c I lamp and with approximately 45 pitch, whereby the polarized component which is reflected into the lamp is polarized on an axis which assures its transmission by the polarizing material at the opposite side of the lamp wall.

10. A polarizing lamp as defined in claim 7 which comprises a reflector of the type which modifies the polarized character of light reflected therefrom, said reflector being positioned opposite said polarizing part of the lampwall and facing said part across the interior of the lamp, whereby the polarized component initially reflected into the interior of the lamp from said polarizingpart of the wall is again reflected to said part and at the same time is modified so that a substantial portion thereof can escape as polarized light of the desired character.

11. A polarizing lamp which comprising an incandescent light source, a lamp wall including a light-permeable portion having an optical surface departing substantially from every surface which can be formed by bending a plane sheet without stretching it along a dimension transverse to predetermined lines of orientation hereinafter specified, and an uninterrupted unstressed substantially permanent coating of noncrystalline dichroic polarizing material on, and

conforming in shape to, said surface, the molecules of said dichroic material being uniformly oriented along said predetermined lines relative to said surface, having substantially the same relation, respectively, to a single geometric axis of reference, adjacent molecules of said material 1 being substantially parallel and said coating uniformly polarizing light at all angles incident thereon, from the interior of the lamp, with polarization uniformly conforming to the pattern of said predetermined lines.

JOHN F. DREYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,400,877 Dreyer May 28, 1946 2,249,061 Styli July 15, 1941 2,263,249 Rogers Nov. 18, 1941 2,185,018 Sauer Dec. 26, 1939 2,041,138 Land May 19, 1936 1,918,848 Land July 18, 1933 2,222,788 Touceda et al Nov. 26, 1940 1,873,951 Zocher Aug. 30, 1932 2,104,949 Marks Jan. 11, 1938 2,256,108 Blake Sept. 16, 1941 2,018,963 Land Oct. 29, 1935 2,252,324 Land Aug. 12, 1941 FOREIGN PATENTS Number Country Date 803,464 7 France July 6, 1936 48,249 France Aug. 10, 1937 (Addition to No. 803,464) 472,232 Great Britain Sept. 16, 1937 603,326 Germany Sept. 27, 1934 OTHER REFERENCES Photography by Polarized Light, Eastman Kodak pubL, April 1936, (4-36-CH-10) pages 9, 14.

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