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OPTICAL PROJECTION
A TREATISE ON THE USE OF THE LANTERN IN
EXHIBITION AND SCIENTIFIC DEMONSTRATION
BY
LEWIS WRIGHT
AUTHOR OF 'LIGHT: A COURSE OF EXPERIMENTAL OPTICS'
5TH EDITION
RE-WRITTEN AND BROUGHT UP-TO-DATE BY
RUSSELL S. WRIGHT, M.I.E.E.
IN TWO PARTS
PART I
_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_)
* * * * *
{v}
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._
* * * * *
{vii}
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
{viii}
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
* * * * *
{1}
OPTICAL PROJECTION
A TREATISE ON THE USE OF THE OPTICAL LANTERN
CHAPTER I
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_.
* * * * *