The art of projecting. A manual of experimentation in physics, chemistry, and natural history with the porte lumiere and magic lantern

Preface To The Second Edition

Si \ci'. the first publication of this book the author has received so many commendatory letters from many parts of the world that he is fully persuaded that the book met a real want; and a sunbeam is now made useful in school work and in the study of phenomena in many places where no substitute is practicable. In preparing a new edition, some things have been added which it is hoped will make the book still more useful to such as consult it. Two things may be specially mentioned here: the electric lamps and lights for projection purposes, and the production and phenomena of vortex rings. Of the former there is pointed out what is at present practicable, and of the latter it may be said that the vortex-ring theory of the constitution of matter has so much philosophical as well as scientific importance, and the phenomena presented by vortex rings are so curious and unexpected, that the author has felt warranted in presenting what he believes to be the most complete series at present known, especially as he believes himself to be the discoverer of a considerable number of them.

Several small treatises on the management and use of lanterns have been published lately, and may be had on application to almost any of the larger dealers in physical instruments and lantern transparencies. It was not thought advisable to add anything on that subject. An excellent manual for experimental work with the lantern has been published by Lewis Wright, which everyone interested in such matters should have, especially as many of the experiments described in it can be done as well or better by the use of a beam of sunlight, — the use of a beam of sunlight for projection being the peculiar province of this book.

A. E. DOLBEAR.

Index

Absorption spectra

Acoustic curves . . .

Air thermometer . .

Animalcule cage . .

Arc light, To project .

Biaxial crystals . . .

Bubbles.

Bubbles, cohesion of .

C'alorescence ....

Camphor <>u water • 'amera obscura . . . < landle power . . . name, To project

( lapillarity

( austics \\ reflection

" " refraction Chameleon top . . . ( Ihemical tank . . .

'• reactions Chladni's experiment Chromatic aberration ( ihromatic aberration, 1

ii'f-' of

Chroinatrope .... cloud formation . .

Cohesion

Cohesion figures . . ( nil:-.- lantern . . .

Color- of thin Minis .

Concave mirror, To

with ....

Convection in water

Condenser : its u-;- ( on\ ex mirrors . . . ( 'nun's apparatus . . ( Irystalline substances larized light . .

Darkened room . . .

I diagrams on mica . .

Dia magnetism . . .

Diffraction

Disk- for study of color

Dispersion

Distortion

Divisibility of matter .

I >ouble refraction . .

Double salts. Prepared DriMiiiuoiid light . .

jio

111 61

ltl 33

10;

168 140

i;

LOO

1 15 i;

n

lor

Eidotrope

Electric light

•• To project .

Electric spark, lo project

Elements, Spectra of . .

Etching upon glass . .

Films, Vibration of . .

Floating magnets . . .

16/

Fluorescence

Focal length of lenses .

Focusing

Fountain, Illuminated .

'.Hi

Fraunhofer's lines . . • .

( rases for lime light . .

(.host . •

M

clue, Marine

1, 155

Ileliostat

1 52

si

Illumination, fnten-dtv of

[mages formed by lenses

ion

Incandescent electric lamp . . h'>:{ " " " lamp til-

aments 164

Incandescent electric tamp,

( urrents for 164

Interference 71

Interlacing lines 70

Kaleidoscope 88

Kaleidophone •">"

Lamps, Electric arc . . 159, 160

" Incandescent. . . . 163

Landscape projection . . . . 170

Lanterns 14, Is, In

Electric lfil

19 33 23

Ligl

Magnifying power Mountings for . .

Intensity of

INDEX.

Light, Magnesium . .

Lime ....

( 'imposition of, 100,

" Polarized . .

Lissajous' experiments

Mach's experiment Magnetism ....

Magnetic phantom . .

Manometric flames Marine glue ....

Megascope

Melde's experimeni Microscope, Solar . .

attachment Minute substances . .

Mirage

Monochromatic light .

.New Ion's disk " rings

Objective

Objects lor projection

< Irgan pipe . . . .

Opeidoscope . . . .

< Outline drawings . .

Overtones . .

Persistence of vision . . .

Pepper's j.rhost

Plateau's (experiment) . .

Polarization of light . . .

Porosity

Porte Lumiere, To make .

its use . .

Porte Lumieres, various pat terns

Projection with single lens " " condenser .

" of large apparatus,

" Apparatus for ver-

tical

10 I Reflections, Multiple

11 j Refraction . . . .

Resultants . . . .

, 136 127

150 150

[00 49 133

Pyrometer 14;")

Rainbow ....

Reactions, ( 'hemieal Reflections ....

Salicine crystals . . .

Screens

Sciopticons

Silver crystals ....

Singing flames ....

Sinuous lines

sizes of objects and of imaj

To compute ....

Soup bubbles, Persistent " Tension of Sodium line in solar speetri Solar microscope . . . spectrum .... spectacle glasses, To lest Spheroidal form ....

Spectra, Methods of proji

Spectrum analysis . . .

'• of sodium . .

" " •' lever- Starch

Stroboscope

Sympathetic vibrations

Thermometer Total reflection Tuning forks .

it is 53

ill ior

170 100 u<

153 119 121

1 ■.'■.' 134 139

111 114

Vibrations of strings .... 59

Vision, Persistence of ... 139

Vortex rings, To produce . . V,-i

" " their phenom

ena 174

Water, Decomposed .... 153

" Maximum density . . Mil

" Refraction of .... 97

" Total reflect ion in . . <M

Waves in water til

Whirling table attachment . 77

Zoetrope HO

THE ART OF PROJECTING.

A magnified image of a picture, or of any phenomenon, when thrown upon a screen by means of sunlight, and lenses, or with a magic lantern, is called a projection.

When sunlight is to be used for this purpose, it is necessary to have some fixture to give the proper direction to the beam. The hrfinstat and the porte lumiere are the devices in common use. The latter was the earliest form, and was invented by Gravesand, a Dutch professor of natural philosophy, in the early part of the last century. It was afterwards reinvented by Captain Drummond, an Englishman, who called it the hcliostat. The latter term is now only applied to an automatic arrangement, by which a mirror is moved by clock-work in such a way that a beam of sunlight reflected from it may be kept in one direction all day, if it be needed so long. Silberman and Foucault have each devised very satisfactory instruments, but they are too costly to be owned by any but the wealthy ; the catalogue price of the cheapest of these being five hundred francs. C. Gerhardt, of Bonn, however, makes a small one, carrying a good mirror three inches in diameter, for twenty dollars.

THE PORTE LUMIERE — HOW MADE.

The porte lumiere is made of various patterns by different makers, but the differences consist chiefly in

2 THE ART OF PROJECT! XG.

the devices for giving proper movements to the mirror. Their cost is from ten to twenty dollars according to their size, workmanship, and attachments. On the opposite page are engravings of several such as are in the market. It is recommended that one be purchased at the outset, if it can be afforded, but as many who would be glad to work with one may not be able to purchase it, directions will be given for making one that will enable any person who is familiar with the use of carpenters' tools to make one at a trifling cost that will answer for many purposes.

The room in which the porte lumiere is to be used must, of course, be one into which the sun can shine. A room having windows only upon the North side, evidently cannot be used at all for such a purpose ; one having windows only upon the East or upon the West side could be used only in forenoon or afternoon ; while one with windows looking to the South can be used nearly all day. Choose then that window where the sun is available the longest, and opposite to which can be stretched the screen to receive the projections upon. Next, take a well-seasoned piece of pine board a foot or more in width, and an inch thick when dressed ; cut it to the length of the width of the window sash, so that it may fit into the window frame, and the sash be brought down upon it ; this will keep it tightly in place. With the compasses, scratch two concentric circles in the middle of the board, one with a radius of four inches, the other with a radius of four inches and a half. Saw out the inner circle completely, and cut the other but one half through the board, and then cut away, making a square rabbet, as shown at b b. Next, take a round piece of inch board of the same diameter

Hawkridge

PORTE LUMIERES.

Adams's.

PORTE LUMIERES.

PROJECTIONS FOR THE SCHOOL-ROOM.

as the outer circle (namely, nine inches), cut a rabbet upon one side of it so that it will nicely fit into the hole of the larger board, as indicated at c c.

Make the worked edges, and touching surfaces, quite smooth; but the outer edge should be made a trille smaller than the hole, in order to allow the disk to turn freely round in it ; then the hole may be cut in the disk to receive die lens, four or five inches in diameter, whichever it may chance to be.

Procure a nice piece of thin looking-glass, twelve or fifteen inches long and five inches wide. Fasten it to a back of wood made a little larger than itself, with broad-headed tacks, or bits of wire driven in and the top bent at right angles. This back will need to be an inch thick at the bottom, but may taper like a shingle to the top, where it need not be half an inch thick; 111 is the mirror and // is the back in the figure adjoining.

A common desk hinge // may be used to attach this mirror- mounting to the part c in the figure below. It must be so fastened that the mirror may swing through ninety degrees from a horizontal plane. The accompanying figure will be sufficiently definite to enable any one to make the whole instrument. When the mirror is securely fastened to the part <; the whole can be inserted in the board b b and buttoned in, as is shown at /' and b ; these buttons must not bind upon the part c, as this must have an easy rotation in its place, though they need to be tight in the board b ; three of them will be enough. Again, a string must be attached to the end of m, passed through a small hole in <r, and tied to a tight-fitting thumb peg at d. As the peg is turned the mirror will be raised or lowered. A short lever v must be made fast to some part of c with which to turn the whole fixture around as the sun moves. The ray of light / can then be always kept where it is wanted.

If the window-sill be no more than two or three feet from the floor, it will be better to have this fixture either put into a window shutter, or to remove a pane of glass at the proper place and fasten the board b b into it. In this case it will be necessary to have a cap to place over the hole when it is not in use.

The lenses will need to be purchased ; and for a beginning I recommend a cosmorama lens five or six inches in diameter and with a focal length of eighteen or twenty inches ; a plano-convex lens of two and a half or three inches diameter and eight or nine inch focus ; also a pocket botanical glass with focus of one or two inches. These three lenses should cost no more than six dollars, if the two former are unmounted. If one has got a magic lantern, or a sciopticon, the lenses in that will answer admirably. Take one of the glasses of the compound condenser and fasten it into the orifice of ihepor/e lumiere with its convex side out ; then, taking out the front lenses, hold them with one hand in the path of the divergent beam of light from the porte lumiere, and distant but four or five inches from it, and with the other hand hold some object between it and the larger lens ; by moving the lens or the object a little, a sharp outline of it will be observed

PROJECTIONS FOR THE SCHOOL-ROOM. 5

upon the opposite wall, and then will be seen what further conveniences will be wanted, such as curtains, screen, table, mounting for lenses, etc.

THE DARKENED ROOM.

Exhibitions with the stereopticon are almost always given at night, and there is no trouble from exterior light ; but the illustrations and demonstrations which are part of the work of schools and colleges need to be given in the daytime, and this neces: itates a provision for shutting out the light which will interfere with the experiment.

The light may be excluded from a room by tight-fitting shutters, or with curtains It is very difficult to make shutters so tight that all light is excluded by them. It can be done much better and cheaper by having some frames made the size of the window frames, and covering them with what is known as enamelled cloth, such as is used in upholstery and carriage trimming. These should fit tight enough in their places to remain when placed.

The same kind of cloth can be attached to common curtain fixtures, and rolled up and down as wanted ; but it will be found that a great deal of light will pass by the edge of these curtains. This can be obviated by tacking strips of the same material a foot wide to the side of the casing, so that the curtain will roll down inside of the strips. When sunlight or the lime-light is used, it is not always necessary that the room should be totally dark ; and, indeed, some of the best experimenters think it a part of their success that their work is done in a room that is light enough for one to see to read a newspaper. Yet there are some experiments which require that extraneous light be shut out from the room : for instance, the projection of the Fraunhofer lines in the spectrum of the sun, and the phenomena of diffraction. For these, and the like, the darker the room the better.

The curtain in the window that holds the porle lumiere will need to have a hole cut in it large enough to allow the beam of light to come through, and to permit the hand to give proper motions to the mirror. A flap should hang over this when sunlight is not wanted, and the electric light or the lime-light is used instead.

THE SCREEN.

The white surface that receives the projected picture is called the screen, and it may be a white finished wall, or white cloth properly mounted. The back of a large wall-map makes a good screen if the light is used in front of it, and only a small disk of light is needed, but the backs of such maps are apt to get discolored, and to become so dark as to be useless. They ma) then be made white by painting them with whiting, mixed in a thin solution of glue.

For a parlor exhibition, a common sheet may be hung against the wall, or between the folding doors, and the lantern used on either side. If the lantern is placed back of the screen, the latter should be kept wet, as it is made more translucent, and the pictures will appear brighter.

When the porte lumiere, the electric light, or the oxyhydrogen lantern is used, a much larger screen will be necessary. They are sometimes made twenty-five feet square or more, but for most purposes a screen fifteen feet square will be large enough. Common bleached sheeting, ten quarters wide, can be bought in most towns. A strip of this, ten yards long, cut into two

PROJECTIONS FOR THE SCHOOL-ROOM. 7

pieces of equal length, and having the selvedges sewed together, will make such a screen with but one seam. That these edges may come together, but not lap, let the sewing be done with what is called the carpet stitch. Seme loops of tape or small rings may be sewed into the corners, and it may be hung upon nails driven into the wall at the proper places.

It is often convenient to have the screen so mounted as to permit it to be rolled up when not in use, and various devices have been invented to effect this. Perhaps the neatest is to have a roller at the top containing a strong spring, which is wound up when the screen is pulled down, — a large curtain fixture. A wooden roller sixteen feet long is likely to sag in the middle, unless it is made so large as to be cumbersome. It is best to have one made of tin tube about three inches in diameter.

A screen can quickly be put up in any room by procuring two strips of board, two or three inches broad, and long enough to reach from the floor to the ceiling. Fasten the sides of the screen to these, and then wedge them tightly between the floor and the ceiling. A portable frame which can be adjusted to various heights may be made by having two such strips for each side : one of them to be provided with a collar at its end for the other to slide through, and to be made fast together by a thumb-screw through the collar, as in the figure.

This will permit one to adjust it to different heights to its limit of eighteen or twenty feet, while by resting the foot upon chairs or tables a still higher room would be provided for.

THE ART OF PROJECTING.