Fig. 42.--Hughes' Short-Range LanternFig. 42.—Hughes' Short-Range Lantern.
In deciding upon the type of body to be purchased the main considerations to be borne in mind are: (1) The type or types of illuminant to be used, a powerful arc lamp for example requiring a larger body than is necessary for a weaker radiant; (2) the size and position of the lens to be carried, a Petzval objective of say 3 inches diameter which has to be supported at the end of a long brass mount for long-range work obviously demanding a body of greater strength and rigidity than is required with a 6-inch focus lens of 2 inches diameter; (3) price.
Fig. 42 shows an extremely good lantern body for short-range work made by Messrs. Hughes, the illustration depicting the instrument complete with a 'Luna' methylated spirit lamp, though, of course, any other illuminant suitable for a small lantern could be used instead.
This lantern illustrates well one point that has already been emphasised as important, viz. the ventilation of the condenser. It will be noticed that this is placedoutsidethe body of the instrument instead of inside as is usual with larger bodies, and that wide slots are cut in the condenser mount to allow free escape of steam.
Other points of this excellent design are the screw adjustment to the slide stage (facilitating the use of special slides, such, for example, as those illustrating the movements of the planetary bodies which sometimes involve the use of extra thick frames) and a simple but efficient tilting arrangement to the base.
Fig. 43.--Long-Range LanternFig. 43.—Long-Range Lantern.
Such a lantern is hardly suitable for a powerful arc lamp or limelight jet, or for heavy long-range lenses, but is a very good typical instrument for use in moderate-sized halls, and a lantern of this general type is usually found in lantern catalogues, though, of course, the exact designs vary according to the ideas of the manufacturer. Of lanterns for long-range work a good example is perhaps Messrs. Newton & Co.'s 'Intermediate' pattern (Fig. 43).
This again is only typical of many others by the various makers, but the principal points are common to all. These are: (1) The large and well-ventilated body; (2) the longbaseboard; (3) the strong and massive brass front necessary to carry the large long-range lenses; (4) the velvet curtain at the back to close in any stray light from a powerful arc lamp.
Fig. 44.--Connections for a Bi-unial LanternFig. 44.—Connections for a Bi-unial Lantern.
The two foregoing designs are perhaps sufficiently typical of lantern bodies in general to make further detailed description of individual designs unnecessary; but reference should be made to features which special requirements may render advisable.
Under this heading mention must be made ofBi-unialsor Double Lanterns, as used for the once famous 'Dissolving Views.'
A bi-unial lantern consists essentially of two different instruments, each complete with its limelight jet or other illuminant—front, condensers, objective, &c., usually mounted on one body—and with some arrangement for 'dissolving' or turning the light in each lantern gradually on and off.
Fig. 44 shows the back view of such a lantern with two limelight jets and dissolving tap, this piece of mechanism (shown below in the illustration) being so arranged that when the lever is horizontalbothlanterns are on full, but moving the lever either way cuts off the gas supply to one lantern. In the case of limelight the tap should always operate by cutting off the oxygen supply in advance of the coal gas (in order to avoid a 'snap'), and the latter should never be cut off entirely, but a small bead of flame left to keep the jet alight, until the lantern is required for the next slide.
This is usually arranged for by means of a bye-pass, and a bye-pass is sometimes provided on the oxygen side as well, but is usually discarded in practice.
A bi-unial lantern can be worked in the same way with acetylene gas, but with the electric arc it is impossible to turn the light on and off gradually, and in practice dissolving must be done by keeping both lanterns fully alight, and using a dissolving shutter, that is a movable shutter that covers each objective alternately. The same arrangement must be used with other illuminants, such as oil, only in this case the lanterns must be mounted side by side, on account of the tall chimneys. With oil lamps the arrangement answers fairly well, the dissolving fan, as it is termed, being made with serrated edges which give thegradualobliteration required; but with the electric arc the extremely sharp definition becomes a serious difficulty, and a good dissolver for this illuminant has never yet been found, though, in view of the fact that dissolving views are more or less a thing of the past, the matter cannot be regarded as important.
The advantages claimed for a double lantern are two: first, a 'Dissolving' effect by which one picture fades gradually into the next, and which is supposed to be more pleasing than the movement of a carrier; and second, 'Dissolving Effects' can be shown, such as exhibiting a landscape by day and changing it into a moonlight scene, or bringing on the appearance of a snowstorm, which can easily be done by means of a roller slide, with minute perforations shown in motion by the second lantern while the landscape remains on the screen from the first. In the days when dissolving views were all the vogue, a third or even a fourth lantern has been added for more complicated effects, and at the famous Polytechnic demonstrations of years ago, I believe that as many as six were sometimes employed.
In these days of the cinematograph it is doubtful how far interest in such effects could be revived, and a lantern hasgradually come to be looked on more as an instrument for showing illustrations as required by the lecturer rather than as a pleasing exhibition in itself, and as dissolving views have lost their attraction, the double or triple lantern has been relegated to the limbo of antiquity.
Fig. 45.--Beard's Circulating Water TankFig. 45.—Beard's Circulating Water Tank.
Among other 'special' lanterns should be mentioned models made with water-cooled stages, for use with very delicate slides. This elaboration is not necessary with ordinary slides and illuminants of moderate power, but where very delicate slides, such as specimens of natural colour photography, have to be shown, it is an advisable precaution to pass the beam of light first through a tank of water in order to absorb the heat. Lanterns intended for this work are usually constructed with a kind of double stage, a glass trough of water fitting into the rear aperture and the slide-carrier into the front one. Such an arrangement answers quite well for most purposes, but for extreme cases lanterns are equipped with a trough connected to a large outside tank and complete circulatory system, after the manner of the cooling tank of a gas engine.
Such a lantern, constructed by Messrs. Beard, is illustrated in Fig. 45, and it will be seen that in this instrument the water trough is placed between the lenses of the condenser.This is a very good position, as the beam of light at this point is, or should be, parallel, whereas between the condenser and the slide it is convergent, and therefore a condenser of a larger diameter than the slide must be employed in the latter case if the trough is of considerable width.
While dealing with 'Special' lantern bodies, we should perhaps just mention here the numerous pattern lanterns made for the demonstration both of lantern slides and of Scientific Phenomena, such as the projection of insect life or other microscopic objects, polarised light experiments, electrical apparatus, opaque objects, &c. A detailed description of these lanterns and how to use them belongs to the second part of this work, as also does the popular cinematograph; but educational institutes, and even boys' clubs, when considering the purchase of a lantern, might well reflect whether it would be advisable to spend a little more money in the acquisition of an instrument which can be utilised for a variety of purposes.
LANTERN BOXES, STANDS, READING LAMPS, ETC.
Having now discussed all the essential parts of a lantern, the next points to be considered are those of lantern boxes and stands. It is best to take these together, as more often than not a lantern is arranged to stand upon its box during use, and the plan is both convenient and simple. The whole question is one to be settled upon its own merits in each individual case. Sometimes neither box nor stand is wanted at all. The lantern is put away into a locked-up cupboard or other safe place, and used upon a permanent support or (as is often the case in a church) from a gallery at the back.
In most cases, however, a box of some sort is desirable, and the two main considerations are strength and simplicity.
All patent arrangements, such, for example, as those in which the sides of the box fall down and provide trays for the slides, are beautiful in theory, but cannot be recommended in practice. A good, simple and substantial box is what is required, preferably painted black, and provided with strong handles.
One addition may be permitted, viz. a tilting top. Some means for tilting the lantern is always advisable, as it is seldom convenient to raise the instrument to the level of the centre of the screen, and a slight upward elevation does not appreciably distort the image. This arrangement for tilting may be either embodied in the lantern itself, as for instance in the instrument shown in Fig. 42, or may be provided for on the box or on the stand, if a stand is used.
It is, perhaps, an elaboration that may be regarded as not strictly necessary, as a book or two or other article may be placed under the lantern base as required; but a tilting arrangement is so convenient that it can be strongly recommended, and the addition is not expensive.
For large, long-range lanterns a strong deal box, on which the lantern can stand, is usually all that it is desirable to purchase in the way of a support. A good solid table can usually be found, which will do all the rest, as it must be remembered that a slight tilt at a long range means a good deal of total elevation.
Where this is not procurable a stand must be provided, and this for a large lantern should be strong and rigid. Anything in the way of a collapsible tripod should be avoided, but such an arrangement as Fig. 46 is quite good and rigid enough for all practical purposes.
For asmalllantern a tripod stand is quite suitable, though care must be taken that one of the legs does not get kicked, either by accident or design, or the result may be a catastrophe.
Slide Boxes.—On this subject not much need be said. The variety of patterns on the market is endless, some being designed from the point of view of safe transit by post, others for convenience of storage and classification. It is essentially a case where each individual user must use his or her taste, and in any case the question of the box is one for the owner of the slides rather than for the lanternist.
Fig. 46.--Quadruple Lantern StandFig. 46.—Quadruple Lantern Stand.
Reading-Desks, Lamps, and Signals.—Some form of reading lamp for the lecturer is generally considered to be part of a lanternist's equipment, and the most usual pattern is fitted with a candle, after the manner of a carriage lamp, or else constructed to burn colza or other vegetable oil, such as supplied for cycle lamps. Oil gives the brighter light, but is apt to get spilled in transit, hence a candle lamp is the moreconvenient for a travelling lecturer, while oil is to be preferred if transport is not a factor to be considered.
These lamps are usually constructed with a red flashing signal at the rear, actuated by a simple lever, by which the lecturer can communicate his wish for a change of slide, &c., to the lanternist (Fig. 47).
Fig. 47.--Reading LampFig. 47.—Reading Lamp.
There are various other devices used for the same purpose, such as a castanet, to be held in the lecturer's hand and clicked when necessary, an electric bell to ring in the lantern box, &c. If this latter is used it is usual to remove the gong, the buzz of the hammer being sufficiently loud without it. Some lecturers again prefer to use no such apparatus at all, but simply to say 'Next slide' as required, or to tap on the floor with a pointer, and the choice of a suitable means of communication between lecturer and lanternist must be largely a matter of individual selection. More elaboratereading-desksare also supplied by most makers, but here again judgment must largely come into play in what is hardly a technical matter.
SCREENS AND SCREEN STANDS
The best of all screens for lantern purposes is undoubtedly a smooth whitewashed wall, and this is now provided in many halls where lantern exhibitions are usual. In places where this is not practicable the next best substitute is a canvasscreen, which rolls up and down (Fig. 48). This can be obtained from any good maker, but again can only really be used as afixturein the hall where the lantern is to be used. It can, however, be fitted into a wooden box which can be painted or varnished to suit the other architecture, and the provision of such a screen is to be strongly recommended whenever possible. If portability is required, a linen or calico sheet that can be folded up is necessary, but this can never be hung absolutely flat, and also loses a considerable amount of light by transmission.
Fig. 48.--Roller ScreenFig. 48.—Roller Screen.
A so-called 'transparent' sheet is made of very thin linen, and intended to work with the lanternbehindit, showing the picture through the linen to the audience on the other side, but this is seldom used except in the open air for religious or political meetings, &c.
Anopaquesheet can be had in one piece up to 9 feet square; larger sizes than this must have at least one seam, and most skilful sewing is necessary, especially with large sheets consisting of several strips sewn together.
Sheets such as these are usually supplied with either eyelet holes round the edges or else linen tapes sewn on, and the exact method of hanging must be left to circumstances.
In the case of a small sheet it will be sufficient to stretch it at the four corners, and this can often be done by screwing into the walls or some convenient girder two screw eyes and similar eyes into the floor, all four being considerably farther apart than the size of the sheet.
Fig. 49.--Portable Screen StandFig. 49.—Portable Screen Stand.
A stout cord being then passed through the two upper eyes, long enough for both ends to reach near the floor, one end of each can be fastened to the two top corners of the sheet and the latter drawn up, the two bottom corners being afterwards stretched and tied down tightly to the lower eyes. In the case of large sheets this hardly suffices, and it will be found necessary to fasten the sheet at intervals all round or it will exhibit awkward creases, and this again is a matter where the lanternist must use his own initiative according to the possibilities.
In some halls the erection of a sheet in the way above described is a sheer impossibility, and in such cases a frame must be made by nailing strips of wood together, or better by utilising a portable screen stand (Fig. 49).
These stands are usually made of bamboo, with short brass connecting tubes, and the method of using them is so obvious that a description need hardly be given. The screen frames are supplied by all the leading opticians, but an intending purchaser would be well advised to see one erected before ordering. I have actually seen a 12-foot screen frame offered for sale that was too weak to carry its own weight, let alone the weight of the sheet!
THE PRACTICAL MANIPULATION OF A LANTERN
Having now described the optical lantern in its various forms and the more important accessories, we come to the question of practical manipulation. In making arrangements for an exhibition the first thing to be seen to is to ensure that every accessory that will be required will be there, and the best plan is to make a complete list of all sundries to be provided. Such items as string (for the sheet), lime tongs if limelight is used, pliers for changing carbons if the arc is to be the illuminant, screw-driver, matches, thekey of the lantern box, and other similar items, are likely to be left behind unless such a list is made and carefully checked. On arriving at the hall, the first thing to be done as a rule is to get up the sheet, after which the professional operator generally begins to feel happy again.
The next thing, if it has not been done first, is to determine the position of the lantern, and this, as has been explained in Chapter VII, is a matter of the size of picture to be shown and the focus of the objective.
It is a mistake to show too large a picture; a little 'white' round the edges is a good thing, and it is better to have a small disc well illuminated than a large one less bright. Convenience, however, must also be considered, and it is often justifiable to go back a few feet farther than other considerations would dictate in order to place the lantern in a gallery or other spot where it is out of the way.
Having fixed the position of the lantern, it should be got into place, the cable or tubing connected or whatever else is necessary, according to the illuminant to be used. It should then be lit up, the flasher of the lens opened, and the lightcentred sufficiently to produce some sort of disc upon the screen. (It is, of course, presumed that the lenses, &c., have previously been cleaned.)
A carrier should now be placed in the stage and a slide inserted into it, and the method of doing so requires a little explanation. The slide must be placed in the carrier upside down, as will be obvious to anyone who has studied Chapter VII, but in addition to this it must be turned the correct way, otherwise the picture will be reversed from left to right. This in the case of certain subjects, such as a copy of a picture, may not greatly matter; but in slides depicting buildings or landscapes with which the audience may be familiar, or worse still, printing or writing, is a serious blunder.
Slides made by a commercial firm will usually be 'spotted,' that is to say, will have two white spots on the face of the slide when the latter is viewed in its correct position, and at the top. The slides should be turned upside down and placed in the carrier with the spots, of course, now at the bottom andtowards the condenser.
If a slide is not spotted it should be viewed as it is to appear on the screen, and then placed in the carrier with the face that was towards the operator as he viewed it turned to the condenser, and of course inverted.
The above remarks apply only in cases where the image is thrownonthe screen; in the comparatively rare instances where it is shownthroughthe latter the slides must be turned round laterally, but of course still inverted. The slide having been placed in the stage it should be 'focussed' by racking the objective in or out, and if necessary pulling out the draw tube as well until the image on the screen is sharply defined. So far the light has only been roughly centred, sufficiently so to enable the slide to be focussed, and to complete the operation both slide and carrier should next be taken out of the lantern, leaving a clear disc on the screen, and this disc may resemble any of the appearances shown in Fig. 50.
If it resemblesAthe light must be moved to the left, if likeBto the right, likeCit must be lowered, likeDit must be raised, always moving it to the side opposite to the dark shade until this is central on the disc. If it now resemblesE, the light must be moved nearer the condenser; if, on the contrary, the centre is dark, it must be drawn back until finally the circle should be as nearly as possible clear and bright all over, as atF.
Fig. 50.--Adjustment of the LightFig. 50.—Adjustment of the Light.
It is important to note that this adjustmentcannotbe properly made while a slide is in position, and neither can it be made until the lantern has been focussed, so the above procedure is the only way to get a satisfactory result. With some of the larger illuminants, such as a paraffin-oil lamp, there are no centering adjustments, the size of the radiant rendering exact centering unnecessary, and generally speaking the smaller the luminous point, the more exact must the operation be.
In the case of such illuminants as acetylene or limelightcare must be taken that they are turned fully on before centering, otherwise turning on the fuller amount afterwards will raise the position of the luminous spot.
The centering achieved, the slide carrier may be replaced, the first slides placed in position, the remainder arranged in their proper order, the system of signalling with the lecturer determined, and all is ready.
If there is still an interval before commencing, the light may be switched off or turned out, or in the case say of limelight, turned down very low until wanted.
It is of extreme importance to see that all the slides are in their right order, though the duty of seeing to this usually rests with the lecturer rather than with the operator. I remember hearing of one lecture on the life of Queen Victoria, when the lecturer announced, 'The next picture will be a photograph of the Royal Prince who for many years shared the Throne with our gracious Sovereign.' At the words the operator brought on the next slide, which proved to bea restored specimen of a prehistoric monster(tableaux!). Such mistakes 'bring down the house,' but in serious lectures, and especially at religious services, cannot be too carefully guarded against.
Mention has already been made of the liability of moisture to condense on the surfaces of the condensers or slides, and to avoid this, so far as the condensers are concerned, it is well to light up say ten minutes before the lantern is actually wanted, or alternatively to take out the condensers and thoroughly warm them in front of a stove, or to place them wrapped in a cloth on hot-water pipes. The slides should in the same manner be warmed before using and should be finally held above the lantern or placed on the top, if this is flat, the last thing before being placed in the carrier. If these precautions are omitted, on a cold night the first surface of the condenser will become so covered with moisture as to almost obscure the slide, and this will quickly disappearwith the heat of the lantern. Next, the two inner surfaces of the condensers will behave in turn in the same way, and will take considerably longer to clear, especially if the ventilation of the condenser is poor; then the fourth surface will take up the running, and finally, when the lanternist is congratulating himself that the trouble is over, each successive slide will become affected in the same way. With an operator who knows his business, none of these troubles should occur.
Accidents.—These will occur sometimes, even in the best managed exhibition; the rubber tubing feeding a limelight jet gets kinked or trodden on, or a fuse melts if electric light is being used, &c., and out goes the light. In such cases a loud request such as, 'Would you mind turning up the light for a minute, please,' accompanied by a good-humoured laugh, usually allays the fears of 'nervy' people. An operator must never get 'nervy' himself. I have known of more than one fiasco because some little hitch occurred, and two or three timid ladies crowded round and asked anxious questions, till the lanternist lost his head. In one such case the cautious superintendent at a children's entertainment decided that it would be safer not to have the exhibition at all, simply because a regulator was not screwed tightly enough into a cylinder to prevent an escape of gas, only the operator (a somewhat youthful one) had been driven to the verge of lunacy by continual questions of the standard type, 'Are you sure it is safe?' 'Will it blow up?' 'Are you certain you understand it?' &c., &c. More serious accidents, such as the entire lantern getting upset, ought never to occur, and it is up to the lanternist to take whatever precautions he deems necessary to safeguard his instrument. With a juvenile audience, for example, it is often a good thing to arrange a barricade of forms round the lantern and to see that no one comes within it.
Finally, 'whatever is worth doing at all is worth doing well,' and this is as true of lantern exhibiting as of anythingelse. There are a deplorable number of lantern exhibitions given with the sheet hanging in creases, dirty lenses, light poorly adjusted and centred, and occasionally slides shown upside down. A conscientious lanternist should see toeverydetail; slipshod methods, as in everything else, mean poor results.
Printed bySpottiswoode, Ballantyne & Co. Ltd.Colchester, London & Eton, England
Printed bySpottiswoode, Ballantyne & Co. Ltd.Colchester, London & Eton, England
Printed bySpottiswoode, Ballantyne & Co. Ltd.
Colchester, London & Eton, England