US2025861A - Light modifying method and apparatus - Google Patents

Description

Dec. 31, 1935. D, HERUNG 2,025,861

LIGHT MODIFYING METHOD AND APPARATUS Filed March 1, 1932 3 Sheets-Sheet l,

- ATTORNEY-S Dec. 31, 1935. HERUNG 2,025,861

LIGHT MODIFYING METHOD AND APPARATUS Filed March 1, 1952 s Sheets-Sheet 2 I n w Q 3 NVENTOR 116 120 BY C za fauvwdce. 7%

. i, ATTORNEYS LIGHT MODIFYING METHOD AND APPARATUS Filed March 1, 1932 5 Sheets-Sheet 5 MIR nu Willi mu iii!4%?iiiiiHIll iiiiliiiliiliiiii!!!"" HHHIIlllllllll' INVE'NTOR dz z p I 2 7 BY a 2 ATTbRNEYs Patented Dec. 31, 1935 PATENT OFFICE LIGHT MODIFYING METHOD AND APPARATUS David Her-ling, New York, N. Y Application March 1, 1932, Serial No. 596,142

24 Claims.

This invention relates to a light-modifying method and apparatus.

The embodiment of the apparatus illustrated herein varies the light eifect in such a manner as to produce a sound record on, for example, the sound track of a so-called talking moving picture film.

An important object of the invention is the provision of a method and apparatus for such sound recording which eliminates certain difficulties in certain systems now in use.

For example, referring to the variable density system of sound recording in which the entire width of the sound track is used continuously but a in which the density of said track varies longitudinally in accordance with the sound recorded thereon, difficulty is encountered in obtaining the correct development of the film, much of which is spoiled due to uncorrectable over-development V or under-development. Accordingly, it is an object of the invention to provide a method and apparatus for recording sound so that wide latitude in developed density is permissible without resulting in any variation in the sound reproduced from the record.

The variable area system of recording, in which the efiective area measured across the width of the sound track varies in accordance with the sound recorded, avoids the above mentioned objection encountered in the development of the variable density system by reason of the fact that any portion of the sound track is substantially entirely opaque or entirely transparent. However, these substantially entirely transparent areas become scratched or otherwise marred or defaced, or carry unavoidable particles of dust, with the result that when the record is used for the reproduction of the recorded sound, the oil or dirt accumulated in the scratches, and the particles of dust, by varying the quantity of transmitted light, result in the production of extraneous or undesirable foreign noises, such as hissings, clicks and other foreign sounds which are particularly noticeable during a silent sequence.

An effort has been made to eliminate some of these foreign noises in the reproduction of sound recorded by the variable area system by the provision of a movable follower or shield whose purpose is to cover over a portion of the substanit is obviously impossible for such a shield to cover all the transparent area of the sound track, for, if it did so, the entire sound area would be opaque and no sound would be reproduced.

Another object of the invention, therefore, is the provision of a method and apparatus for recording sound in which the full width of the sound track during a silent sequence is wholly opaque, the result being that dust particles-on the track and scratches or other defacements thereon, which may become filled with black dirt or oil, will have no effect whatever in reproduction.

Another object of the invention is the provi sion of a method and apparatus for recording sound on a sound track, such as that provided by a film, in such a manner that no corrective apparatus such as movable light shield followers are required.

A further object of the invention is the provision of apparatus for carrying out the method of the invention which, although extremely sensitive, is, nevertheless, very simple in construction and which eliminates many critical adjustments now generally necessary in satisfactory commercial recording, the sound record produced by the invention being readily reproduced by standard reproduction methods now in common use.

A still further object of the invention is to provide, broadly, a light varying method and apparatus in which light, preferably from a constant fixed source, is modified or varied in accordance with variations in amplitude and frequency of an electric current. As stated, the present embodiments of the invention are particularly adapted to record sound on a light sensitive medium.

Other objects, advantages and uses of the invention will appear hereinafter as the description proceeds, taken in connection with the accompanying drawings which illustrate a preferred embodiment of apparatus for carrying out the invention and in Which- Figure 1 is a view showing partly diagrammatica'lly apparatus constructed in accordance with the invention, part of the apparatus being shown in vertical section in connection with a sound record in cooperative relation with a slotted mask,the film and mask being angularly-displaced for better illustration;

Figure 2 is a face view of the relatively mov- 59' able-coil member of Figure 1 on a reduced scale;

Figures 3, 4 and 5 form a series of vertical elevations of the mask of Figure 1 showing varying lighting effect produced by changes in the apparatusof Fi ure 515 Figures 6, '1 and 8 are diagrammatic views 11- lustrating the variations in the positions of parts of the apparatus of Figure 1 which produce respectively the varying lighting effects of Figures 3, 4 and 5;

Figure 9 is a view similar to Figure 1 on a reduced scale and illustrating a modified form of light varying apparatus;

Figures 10, 11 and 12 are a series of diagrammatic top plan views showing varying lighting effect resulting from changes in the relative positions of parts of the apparatus of Figure 9;

Figures 13, 14 and 15 are a series of front elevational views of the sound record mask illustrating the lighting efiect thereon when the parts of the apparatus are in the positions of Figures 10, 11 and 12 respectively;

Figure 16 is a face view of the movable coil member of the apparatus of Figure 9.

In the embodiments of the invention herein illustrated, means are provided for creating a magnetic field.

Referring to Figure 1, for this purpose a pot magnet modified as hereinafter described includes a pole piece I6 and field coil winding l2.

In the field coil winding flows a direct currentfrom any suitable source, herein conventionally illustrated as including alternating current supply line l4, stepped down transformer l6, rectifying tube l8 and filter 20. The specific circuit is not claimed per se as embodying the invention but is merely one means for supplying the field coil winding with direct current. This circuit may, therefore, be varied in practice as may be desired.

Both embodiments of the invention herein illustrated include a lens or lens system, and in the embodiment of Figure 1 there is provided means for moving the lens or system with respect to a light source herein illustrated as being a fixed source of substantially constant intensity.

As illustrated in Figure l, for this purpose a movable coil 26 is associated with the pot magnet and is carried by a support, such as that shown in Figure 2 which, at its outer portion 28, is secured by screws 30 to the pole piece I l of the pot magnet, the central portion including the disk 32 carrying the coil 26 and being movable with thecoil axially and only axially with respect to the pole piece IQ of the magnet, the arms 34 being sufficiently ilexible to permit such axial movement and being so arranged that they prevent other movement. Carried by the disk 32, preferably centrally thereof, is a lens mounting 36. In accordance with this embodiment of the invention, this lens mounting carries a lens 38, or a plurality of lenses or lens system which for convenience will hereinafter be referred to as a lens, the purpose of which is to converge, preferably to a point focus, hereinafter referred to as the focal point, light coming from the light source hereinafter described.

In accordance with the invention, the pole piece ID of the magnet may be bored to provide a passage 40 for light from any suitable source such as the fixed arc light-42 with which may be associated a parabolic reflector 44. A pair of cooperating lenses 46 and 48 may serve as a condenser between the light 42 and the movable lens 38.

The invention provides, in. the embodiment of Figure 1, means for delivering a varying current to the movable coil 2% for the purpose of moving the lens 38 with respect to the light source 42 for the purpose of producing a variable lighting effect. In the embodiment shown, this variation is in accordance with sound to be recorded on a light sensitive medium, such as the sound track 56 of a moving picture film.

Accordingly the moving coil 26 is in a circuit 6 including the output transformer 52, power ain plifier 54, voltage amplifier 5t, and microphone E8. The invention does not lie in this circuit per se but this circuit is merely a diagrammatic illustration of a form of means for delivering to 10 the movable coil 26 current varying, in the present embodiment, in accordance with sound to be recorded. This circuit is therefore not shown in detail since it may be varied as desired within wide limits. 15 Where the invention is used for recording sound on a light sensitive medium, such as the film 56, the slit 63 is provided in a mask 82 which is located preferably adjacent the film 50 which during recording moves downwardly at a 20 constant velocity, being understood that the portions of the film above and below the slit 6% are shielded from light effects. The. mask 62 is a conventional illustration of any suitable opaque material. 25 In accordance with this embodiment of the invention, the lens or lens system is such that the principal focus is practically a point P. When the coil 25 is in inoperative or neutral position a relatively small wire or other suitable 30 obstruction \l l passes vertically through the focal point. This wire or focal point obstructor 6 5 is, in the modification of Figure 1, held fixed in position by any suitable means and is of sufficient diameter to prevent any light from lens 38 passing beyond the focal point and reaching the mask or film. When the coil 26 is provided with a varying current, however, it moves with respect to the fixed magnet and carries with it lens 38, Whose movement is confined to movement back 40 and forth along its own axis. As a result, the focal point P will at times be to the right of the obstructor 64, as shown in Figure 8, and at times be to the left of said obstructor as shown in Figure 8, and at times coinciding with the posi- 45 tion of focal point obstructor as indicated in Figure 7, the relative position of the focal point P depending upon whether the coil 25 in the magnetic field causes movement of the lens 38 to the right or to the left of neutral position of 59 Figure 7. In the neutral position of Figure 7 all light from the convergent lens 33 is blocked off by the obstructor at the focal point so that no light reaches the mask 52, the shadow or" the obstructor in this position of the parts being sufficient to reach entirely across the slit 56. Consequently, if a sound track film is moving behind the mask, there will be no light to affect it and no latent image will be formed. Such portion of the nega- 69 tive upon development will be transparent; hence, any positive printed therefrom will be opaque. Since the parts are in the neutral position of Figure 7 during a silent sequence, the sound track positive will be entirely opaque for 65 a silent sequence so that no dust particles, scratches that may become filled with oil or dirt, or other foreign matter on the film where it represents the silent sequence, will have any effect whatever in the reproducing apparatus. In this way, objectionable foreign noises noticeable in reproduction of a silent sequence as represented by a transparent sound track area are eliminated by the present invention.

In Figure 1 the sound track or film 50 has 75 hdieeteei h re n e te m 9 eequehee whi h a th a e he secre ion ihdiee ed n ur 1 i m r a ent undevel ed ima e- U eh b ihs d e e an r n ed owe er the ent al r a of he e o d b etne is ble sh is ehes i a t e Po on h en es wa in th n ut a position f ur 7 i e th hen i h 8 of h fi was a sin d wnwardly ca t the slit as above described.

Figure 1- shows he fecal h h ebetrue e in the position which it occupies in Figure 8, that is, with the focal point P further from the film he he o ru t t4- t. n F ure the istance between the focal point P and the obstructor 54 is the maximum, the light and shadow on the mask 52 will be as shown in Figure 5 lhe light area would be a circle having the diameter equal to the length of the slit 59, were it not for the focal point obstructor whose shadow ii} is cast upon the mask. When the lighting effect is as indicated in Figures 5 and 8, the sound track film immediately behind the slot will be affected by bright light on either side of the focal point obstructor shadow 7E3, but the part of the film immediately behind this shadow will not be a fected.

If, now, the lens 33 is moved. by the coil 25 toward the film, focal point P will move a corresponding amount. Figure 6 shows the position of the parts where the distance between the focal point and the focal point obstructor is the same as in Figure 8 but the focal point is between the obstructor and the film. In this case, the focal point obstructor shadow ill will have the same width as under the conditions of Figure 8, but the light area falling on the slot on each side of the central shadow will net; be sufficient on either side of the shadow to reach the end of the slot. The portion of the slot, however, meas ured from one end to the area of light is, however, in relative darkness, being outside the direct areas of light from the lens. Hence, if the lens 38 vibrates between the position of Figure 1 and the position of Figure 6 to produce the sound record indicated in Figure 1 for each Figure 6 position in the positive print there will be an area such as that shown at T2 in Figure 1, whereas for each Figure 3 position there will be no such area.

With the apparatus described there will on the positive print sound record always be a central dark area, more or less wide according to the position of the focal point P with respect to the obstructor 64, this central dark portion extending the full width of the sound track for every coincidence of the focal point with the obstructor.

It is not essential for the production of a sound record that the focal point obstructor be located so that the principal focus of the lens coincides with the obstructor in neutral position of the movable coil. Where this coincidence does not occur in neutral position of the coil but the focal point obstructor is located in advance or behind the focal point, the apparatus is none the less capable of producing the sound record though without the advantage that the focal point ob.-. structor will wholly obstruct light from the film during a silent sequence.

In the modification of Figure 1, the coil has been used to move the lens with respect to the focal point obstructor. In the modification of Figure 9, the apparatus is constructed so that the lens remains stationary and the focal point obstructor is moved by the coil with respect to the ess: This eehetm ieh ha c rta n advanta s eve the et heiure of Fi u e r am l h nertia 9f he coil and h ei h moved b it i reduced b sub itution, of h fo in o structor having a relatively inappreciable weight 5:

direct light is exactly the same whether the focal 15-,

point obstructor is between the focal point and the lens or between the focal point and the slit, In o her We s' h efie e s z o the ro te light area on the mask varies in the construction of Figure 1 by reason of the fact that the light 2Q area base of the cone varies due to shift of the focal point, whereas with the construction of Figure 9, the possible effective diameter of the base of the light cone on the mask remains constant regardless of whether the obstructor is onzs one side or the other of the focal point. In either case, so long as the obstructor and focal point are in coincidence in neutral position, no light will reach the film during a silent sequence.

Referring now particularly to the construction 30, 1

shown in Figure 9, the magnet as constructed is already described. Corresponding to lens 38 however, the lens I38 is carried by a fixed part such as the pole piece Ill]. The coil I26 corresponding to the coil 26 carries the focal point 35;,

obstructor I64 which moves axially of said lens with movement of the movable coil in the magnetic field created by the fixed magnet. Other parts in Figure 9 corresponding to similar par-ts in Figure 1 are identified by reference numerals differing by one hundred from those used in Fi u Where the focal point obstructor Hi l is being moved bodily in the direction of the lens axis, alternately, an equal distance first to one side and then the other of the focal point, a record similar to that shown in Figure 9 on the film 5553 will be produced as a result of the variation in the effective width of the focal point obstructor shadow Hi on the film..

In Figure 13 is shown an elevation of the mask I52 when the focal point obstructor led occupies the gfiitiorl of Figure 10. Figure 13 will be the same as shown if the obstructor in Figure 10 were the same distance from the focal point but 55' to the left thereof as viewed in said Figure 10.

Figure 14 is an elevational view of the mask m2 with the focal point obstructor passing through the focal point, as in Figure 11, in which case the obstructor prevents any light from affecting the film.

Figure 15 shows an elevation of the mask and the light effect thereon with the parts in the position of Figure 12 or when the distance between the obstructor and focal point is the earne s;v as in Figure 1.2 but the obstructor is on the other side, that is, between the focal point and the film.

It is evident that with the apparatus described a sound record will be produced even where the focal point obstructorand the focal point are not 7 in coincidence in neutral position. The nearer they are to coincidence in neutral position, however, the more nearly opaque will be a positive print of the sound record during the silent sequence. Where the focal point obstructor does 7;;

not transmit light, it will always cast some shadow on the slit, and this shadow will be as wide as the slit is long when there is the above described coincidence in neutral position.

It will be understood that where the apparatus Is used to produce a variable lighting effect with regard to the area affected on the film, and where the lens is moved as in Figure 1, the difference in intensity of the light reaching the film, due to the movement of the focal point toward and from the film, will be negligible, first because the lens for this purpose will not appreciably vary the intensity by relatively small movement, and second because the film when developed is either opaque or transparent so thatthe inappreciable variation in light intensity is negligible in practice.

It will also be evident that the construction of Figure 1 may be used for variable density recording by selecting a lens giving relatively great variation in intensity by relatively small lens movement so that the light effect on the film will be greater or less, depending on whether the movable coil moves the lens toward the film or away from it, in which case the focal point obstructor of Figure 1 may be eliminated.

It is evident that various changes may be made in the apparatus as herein specifically described .without departing from the invention as defined by the claims, in which the word lens is used to include a single lens or combination of lenses,

and the word obstructor is intended to include any member Whose function is to obstruct wholly or partially the light coming from the lens. It

will also be understood that reference to a circuit in a magnetic field is not necessarily limited to a construction in which the entire circuit is in such field; and that the word including, as hereinafter used, does not imply an enumeration of all parts of the apparatus but only of the essential parts specified.

It is also evident that the invention is adapted either to register or record variations in amplitude and frequency of an electric current whether such variations are produced by sound or otherwise.

What is claimed is:

1. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a sourceof light, a lens carried by said movable coil and arranged to pass light from said source, a mask having a slit in the path of light passing through said lens, a light obstructor associated with said lens at the focal point thereof, and means for supplying a varying current to said movable coil to move said lens with respect to said obstructor.

2. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a fixed source of light of substantially constant intensity, a lens carried by said movable coil and arranged to pass light from said source, a mask having a slit in the path of light passing through said lens, a light obstructor associated with said lens at the focal point thereof and located between said lens and said mask, and means for supplying a varying current to said movable coil to move said lens with respect to said obstructor.

3. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a source of light, a lens carried by said movable coil andarranged to pass light from said source, a mask having a slit in the path of light passing through said lens, a light obstructor associated with said lens at the focal point thereof, and means for supplying a varying current to said movable coil to move said lens, on its own axis, with respect to said light obstructor.

4. Sound recording apparatus including means 5 for creating a magnetic field, a movable coil associated therewith, a fixed source of light of constant intensity, a lens member arranged to pass light from said source, a light obstructor member associated with said lens at the focal point thereof, one of said members being carried by said movable coil, a mask having a slit in the path of light passing through said lens, and means for supplying a varying current to said movable coil to cause relative movement between said lens member and said obstructor member in the direction of the axis of said lens.

5. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a source of light, a fixed lens arranged to pass light from said source, a light obstructor member carried by said movable coil and normally located at the focal point of said lens, a mask having a slit in the path of light passing through said lens, and means for supplying varying current to said movable coil to cause movement of said light obstructor with respect to said fixed lens.

6. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a fixed source of light of constant intensity, a fixed lens arranged to pass light from said source, a light obstructor member carried by said movable coil and normally located at the focal point of said lens, a mask having a slit in the path of light passing through said lens, and means for supplying varying current to said movable coil to cause movement of said light obstructor in the direction of the axis of said fixed lens.

7. Sound recording apparatus including a fixed source of light of substantially constant intensity, means for creating a magnetic field, a lens arranged to receive light from said source, a light obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium having a slit in the path of light from said lens, and means in said magnetic field for causing relative movement, in the direction of the lens axis, between said lens and said light obstructor ineluding a circuit and means for supplying a varying current thereto.

8. Sound recording apparatus including a source of light, a lens arranged to receive light from said source, a light obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium, said mask having a slit in the path of light from said lens, and means for causing movement of said light obstructor with respect to said lens including a circult and means for supplying a varying current thereto.

9. Sound recording apparatus including a source of light, means for creating a magnetic field, a lens arranged to receive light from said source, a light obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium having a slit in the path of light from said lens, and means in said magnetic field for causing movement of said light obstructor with respect to said lens including a circuit and means for supplying a varying current thereto.

10. Sound recording apparatus including a fixed source of light of substantially constant in- 76 tensity, means for creating a magnetic field a lens arranged to receive light from said source, alight obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium having a slit in the path of light from said lens, and means in said magnetic field for causing movement of said light obstructor with respect to said lens and in the direction of the lens axis including a circuit and means for sup plying a varying current thereto.

11. Sound recording apparatus including a source of light, means for creating a magnetic field, a lens arranged to receive light from said source, a light obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium having a slit in the path of light from said lens, and means in said magnetic field for causing movement of said lens with respect to said light obstructor including a circuit and means for supplying a varying current thereto.

12. Sound recording apparatus including a fixed source of light of substantially constant intensity, means for creating a magnetic field, a lens arranged to receive light from said source, a light obstructor associated with said lens at the focal point thereof, a mask for a light sensitive medium having a slit in the path of light from said lens, and means in said magnetic field for causing movement of said lens in the direction of the lens axis with respect to said light obstructor including a circuit and means for supplying a varying current thereto.

13. Sound recording apparatus including a fixed source of light of substantially constant intensity, a fixed magnet having a field coil winding, means for supplying current thereto, a movable coil associated with said fixed magnet, a lens arranged to pass light from said source, a light obstructor associated with said lens at the focal point thereof, said lens being carried by said movable coil, a mask having a slit in the path of light passing through said lens, and means for supplying a varying current to said movable coil to cause movement of said lens with respect to said light obstructor.

14. In apparatus for making a sound record on a light sensitive medium by varying the effectiveness of a light thereon in accordance with the sound to be recorded, a light source, a lens in position to receive light therefrom, a light obstructor at the focal point of said lens, and means for vibrating said light obstructor rectilinearly in the direction of the lens axis to vary the effective width of a beam of light passing through said lens from said source including a circuit and means for supplying current thereto varied in accordance with the sound to be recorded.

15. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a source of light, a lens arranged to pass light from said source, a mask having a slit in the path of light passing through said lens, a light obstructor associated with said lens at the focal point thereof and carried by said movable coil, and means for supplying a varying current to said movable coil to move said light obstructor in the direction of the lens axis.

16. In apparatus for making a sound record on a light sensitive medium by varying the effectiveness of a light source thereon in accordance with the sound to be recorded, a light source, a lens in position to receive light therefrom, a light obstructorassociatedwithsaid lens at the focal point thereof, and means for producing relative rectilinear movement between said lens and said light obstructor in the direction of the lens axis to vary the effective width of a beam of light passing through said lens from said source including a circuit and means for supplying current thereto varied in accordance with the sound to be 5 recorded.

17. Sound recording apparatus including means for creating a magnetic field, a movable coil associated therewith, a source of light, a lens arranged to pass light from said source, a mask 1 having a slit in the path of light passing through said lens, a light obstructor associated with said lens at the focal point thereof garried by said coil, and means for supplying a varying current to said movable coil to produce relative movement 5 between said lens and said light obstructor. in the direction of the lens axis.

18. Apparatus for varying light effect including a source of light, a lens arranged to converge light from said source to a focal point, a masking 20 device having a limiting effect on the light emanating from said source and passing through said focal point, a light obstructor normally located at the focal point of said lens, and means for moving the lens with respect to the light ob- 25 structor including a circuit and means for supplying a varying current thereto.

19. Apparatus for varying lighting effect including a source of light, a lens arranged to converge light from said source to a focal point, a 30 maskin device having a limiting effect on the light emanating from said source and passing through said focal point, a light obstructor normally located at the focal point of said lens, and means for varying the distance between said lens 35 and said light obstructor including a circuit and means for supplying a varying current thereto.

20. Apparatus for varyin lighting effect ineluding a source of light, a lens arranged to converge light from said source to a focal point, a 40 masking device having a limiting effect on light emanating from said source and converged by said lens, a shadow casting member between said lens and. said masking device in position to cast a shadow on said masking device, and movable to 45 positions on opposite sides of said focal point, and means for varying the distance between said shadow casting member and said masking device including a circuit and means for supplying a varying current thereto. 50 21. Apparatus for varying light effect including a source of light, lens means arranged toproduce a cone of light from said source, a masking device having a limiting effect on light from said source passing through said lens means, a shadow cast- 55 ing member between the lens means and said masking device in position to cast its shadow on said masking device, and means for varying the width of the shadow of said shadow casting member on said masking device by varying the dis- 60 tance between said shadow casting member and masking device, said means including a circuit and means for supplying a varying current thereto.

22. Apparatus for varying light effect includ 05 ing a source of light, lens means for converging light from said source to a focus, a masking device having a light passage therein and having a limiting effect on light from said source passing through said lens means, a shadow casting mem- 70 ber between the lens means and said masking device and arranged to cast its shadow on the light passage therein and being movable toward and away from said focus, said shadow casting device when in the focus casting its shadow entirely 16 focus and movable in operation toward and away from said focus, and means for causing movement of said light obstructor to vary the effective light from said source on a light sensitive surface,

said means having a circuit and means iorsupplying a varying current thereto.

24. Apparatus for recording sound including a source of light, lens means for converging light from said source to a focus, fixed means in the light path for locating light effect from said source upon a light sensitive surface, a shadow-casting member normally in said focus and arranged to cast a shadow on such light sensitive surface,

and means for varying its shadow effect thereon 10,

by moving it out of and toward and from said focus, said means having a circuit and means for supplying a varying current thereto.

DAVID HERLING.

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