Optical Projection. Part 1: the Projection of Lantern Slides

PART I. _the Projection of Lantern Slides_

THE PROJECTION OF LANTERN SLIDES

WITH ILLUSTRATIONS

LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON, E.C. FOURTH AVENUE & 30TH STREET, NEW YORK BOMBAY, CALCUTTA, AND MADRAS

1920

(All rights reserved)

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PREFACE TO THE FIFTH EDITION

The first edition of this work was written by my father, the late Mr. Lewis Wright, and was published in 1890.

The reception that it received testified to the fact that it met a long-felt want, and successive editions were published in 1895, 1901, and 1906.

My father, unfortunately, met his death in a railway accident in 1905, and the corrections and additions to the last edition, which had been to a certain extent prepared by him, were completed and written by myself, and the work as published then was again reprinted in 1911.

As the original text is now thirty years old, it has seemed better entirely to re-write the whole book rather than make fresh revisions, the more so as the last ten years have seen great advances in the science of Lantern Projection, and especially in the developments of Acetylene and Electric Lighting.

It has also seemed best at the present juncture to issue the book in two parts, the first dealing with the Projection of Lantern Slides only, and the second with the Demonstration of Opaque and Microscopic Objects, Scientific Phenomena and accessory apparatus, including Cinematograph Projection.

It must of necessity be many months before this second volume can be produced, for the simple reason that Optical {vi} Instrument Makers have as yet hardly had time to turn round after the war and produce their new models, and therefore any such book written now could do little more than describe apparatus that was on the market prior to 1914.

The present work, therefore, deals solely with the exhibition of Lantern Slides in the Optical Lantern, and as such I trust will be found of value to Schoolmasters, Social Workers, Lecturers, and, in fact, to all who use the lantern as a means of illustration.

RUSSELL S. WRIGHT. January 1920.

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CONTENTS

CHAPTER PAGE

I. INTRODUCTORY 1

II. THE ILLUMINANT 3

III. PARAFFIN-OIL LAMPS, INCANDESCENT GAS AND SPIRIT BURNERS 6

IV. THE ACETYLENE LIGHT 11

V. LIMELIGHT AND THE ACETYLENE BLAST 16

VI. THE ELECTRIC LIGHT 39

VII. THE OPTICAL SYSTEM OF A LANTERN 57

VIII. THE BODY OF THE LANTERN 70

IX. LANTERN BOXES, STANDS, READING LAMPS, ETC. 76

X. SCREENS AND SCREEN STANDS 79

XI. THE PRACTICAL MANIPULATION OF A LANTERN 82

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ILLUSTRATIONS

FIG. PAGE

1. Oil Lamp 6 2. Inverted Incandescent Lamp 8 3. Methylated Spirit Burner 9 4. Luna Lamp 10 5. The Moss Generator 12 6. The A.L. or 'Popular' Model 14 7. Acetylene Jet 15 8. Oxygen Cylinder in hemp cover 17 9. Double Lever Key 18 10. Fine Adjustment Valve 19 11. Construction of Beard's Regulator 20 12. Beard's Regulator 21 13. Regulator and Gauge 22 14. Gas-bags 24 15. 'Blow-through' Nozzles 25 16. 'Blow-through' Jet 25 17. Mixed Jet 27 18. Mixed Jet, Gwyer pattern 27 19. Mixing Chamber of Jet 28 20. 'Injector' Jet 30 21. 'Gridiron' Saturator 32 22. 'Pendant' Saturator 33 23. Fallot Air Blast 37 24. Fallot Air Blast, and Cylinder 37 25. Lime-tongs 39 26. Universal Hand-fed Arc Lamp 45 27. 46 28. Resistance 49 29. 'Scissors' Arc Lamp 51 30. 'Right-angled' Arc Lamp 52 31. 'Westminster' Arc Lamp 53 32. Arc Lamp with Induction Ring 56 33. The Optical System of a Lantern facing p. 57 33A. Optical System of Lantern 57 34. Optical System without Condenser 59 35. Action of Condenser 59 36. Forms of Condensers 60 37. Double Sliding Carrier 62 38. Beard's Dissolving Carrier 63 39. Focussing Action of Lens 64 40. Achromatic Lens 65 41. Petzval Combination 66 42. Hughes' Short-Range Lantern 71 43. Long-Range Lantern 72 44. Connections for a Bi-unial Lantern 73 45. Beard's Circulating Water Tank 75 46. Quadruple Lantern Stand 78 47. Reading Lamp 79 48. Roller Screen 80 49. Portable Screen Stand 81 50. Adjustment of the Light 84

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OPTICAL PROJECTION

A TREATISE ON THE USE OF THE OPTICAL LANTERN

CHAPTER I. Introductory

INTRODUCTORY

Lantern Projection, as commonly understood, may be broadly subdivided into two branches: (A) The Projection of Lantern Slides, and (B) The Projection of Scientific Phenomena, Opaque Objects, Microscopic Specimens, &c., usually referred to broadly under the heading of 'Scientific Demonstration.'

To these two classes may perhaps now be added a third, viz. The Projection of So-called Living Pictures, or, in other words, the Cinematograph. In the earlier editions of this work both A and B were dealt with in the same volume, but, as there are thousands who require to use a lantern for the demonstration of lantern slides only, and who have no interest or concern with Science Projection, it has seemed to the writer that the work might, with advantage, be divided into two portions, Vol. I. dealing with slides only, and Vol. II. with the various adaptations of the science lantern. This present book therefore only deals with the exhibition of lantern slides, and as such it will, I trust, be found to be of real assistance to the ordinary user of the optical lantern, including clergymen, schoolmasters, army and cadet officers, and others {2} who require advice and instruction in the purchase or use of a lantern.

The essential parts of a lantern are: (a) A slide-holder or carrier to hold the slide; (b) a lens to 'focus' it on the screen; (c) a condenser to converge the light upon slide and lens; (d) a source of light or radiant to provide the necessary illumination; and (e) a body or framework to hold the whole together. All possible variations in choice of a suitable lantern relate to one or another of the above parts, and will be treated of in turn; but, fortunately, we have this all-important simplification that every ordinary English lantern slide is the same standard size, viz. 3¼ inches square. Some Continental and American slides differ in one dimension from the above, but not enough to cause any serious difficulty, and the convenient English standard is being gradually adopted throughout the world.

The varieties of slide-holders or carriers are therefore comparatively few and are chiefly concerned with the question of rapidly and easily changing the slides. The choice of a focussing lens or objective is mainly a matter of the size of picture required, and the most convenient distance from the screen for the lantern to be placed. Variations in condensers, which are comparatively small, are usually only a matter of conforming these with the size or type of objective to be used, and should be left to the manufacturer's judgment. The question of a suitable radiant is partly a matter of the amount of illumination required, and partly that of the practical possibilities; for example, if electric current is available some form of electric light is usually the most convenient, as well as the least expensive, but where this is not the case, paraffin-oil, methylated spirit, incandescent gas, acetylene, limelight, &c., are alternatives which all have their uses and must be considered on their own merits.

Sometimes, as for example in the case of a travelling lecturer, a lantern is required fitted with a range of lenses for {3} halls of different size, and also with a variety of illuminants, and this in most lanterns can be easily provided for.

The body is usually a matter of taste and price only, and may range from a simple but efficient shell of Russian iron to an elaborate mahogany instrument with a brass front, screw tilting arrangements and other adornments; but of late years there has been a wholesome reaction against unnecessary finish, and a simple metal body of some description is now chiefly the order of the day. In the foregoing remarks the various parts of a lantern have been mentioned in what I should consider the correct order, starting from the slide and slide-holder, and so to speak building up the rest of the instrument round these items; but I now propose somewhat to vary the procedure and for convenience deal in detail first with the Radiant, or Illuminant.

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CHAPTER II. The Illuminant

THE ILLUMINANT

The first necessity for lantern projection is a strong light, and this can be obtained from a variety of sources, the principal means in common use being approximately in order of excellence as follows: paraffin-oil, incandescent spirit, incandescent gas, acetylene, acetylene air blast, oxyhydrogen (limelight), oxyether, and electric light in its various forms. The ideal characteristics to be sought for are (1) great intrinsic brilliancy; (2) minimum size of luminous spot; (3) freedom from flicker; (4) freedom from smell; (5) absence of any preponderating colour; (6) cheapness; and (7) convenience. There is no question whatever as to which of the available sources of light most perfectly combines all the above if it is available, viz. the electric arc. If a current supply is in {4} the building, this form of lighting easily excels all others, except possibly in the matter of flicker, and even in this respect there is very little fault to be found with it.

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