The preceding chapter described how it is possible to photograph extraordinarily rapid movements and to slow down in projection so as to enable the eye to follow them. Now I will go to the other extreme and show how the very slowest movements can be accelerated and thrown upon the screen in continuous motion. This feature has proved one of the most popular in the whole range of cinematography, for it has enabled the public to follow, within the course of a few minutes, such wonderful and apparently impossible studies as the growth of a plant from the germination of the seed and the appearance of the leaves to the bursting of the bloom and the formation of the seed for the propagation of the species.

The speeding-up of relatively slow movements has become a favourite branch of research among cinematograph workers mainly because it is simple, inexpensive, and comparatively easy. The worker needs to develop only one special faculty. That is patience, for the recording of a single subject may easily extend over a period of a month or so, and the camera has to be kept going night and day to produce a faithful record. It is a field which the amateur can follow very profitably. It puts no great tax on his skill. The risk of failure is slight, and the films thus obtained, if worked out upon popular or instructive lines, are certain to command a ready market.

For this work one may use the ordinary £5 ($25) camera. It illustrates the fact that cinematography is nothing more nor less than a string of successive snap-shots, for the principle is that which is generally described as "one turn one picture." That is to say, instead of the handle being turned continuously as in taking a topical subject, it is moved at stated intervals, and only sufficiently to make one exposure and to jerk the film downwards the required distance ready to receive the succeeding image. It virtually resolves cinematography into ordinary snap-shot or Kodak photography.

This development, like many others widely practised in the moving-picture world to-day, has issued from the Marey Institute. It was there exploited in the usual manner for the study of natural movement and phenomena. In the early days of the present century, even before the picture palace came into vogue, the workers of this institution produced a short length of film showing the opening of the blossom of a convolvulus. Although this film is some ten years old it would be difficult even now to improve upon it. The opening movement of the petals is so steady and perfect as to suggest that the exposure was not intermittent but continuous.

In these particular studies success in the main depends upon the apparatus employed for the periodical exposure of the film and the judgment shown in deciding the lapse of time between the successive exposures. Naturally this varies according to the characteristics of the subject under investigation. A mushroom, for instance, demands exposure at briefer intervals than would be necessary for filming the growth of a grain of wheat. The timing is perhaps the most difficult part of the undertaking, because if it is not gauged to a nicety the movement on the screen is apt to be unnatural, the growth taking place in a series of sudden jerks instead of proceeding slowly, steadily and gracefully. Many a first-class film of this character has been ruined because the interval between the exposures has been too long to bring about the necessary blending together of the motions in the successive pictures. No hard and fast rule can be laid down to guide the worker. Experience and close study of the subject being photographed can alone enable this factor to be determined.

The auxiliary apparatus to ensure the exposures being made at regular intervals need not be of an intricate character. The simpler the means, the more likely is the result to be successful. Clockwork mechanism can be devised to open the shutter at stated intervals, but this system suffers from one serious disadvantage. The mechanism must be wound up regularly, and when a long study is in progress, extending over a fortnight or a month, the worker is apt to overlook this indispensable duty. There is one worker who generally uses a water motor, and has found it very reliable; but it cannot be safely left, and it ceases to act if the public water supply be cut off.

The most reliable agent for such work is electricity. When the Marey Institute first embarked upon these tedious subjects a very elaborate apparatus was employed. It was like a gallows, being in reality a massive wooden frame (see illustration facing page 128) fitted with a pulley. A rope passed over this pulley, and to one end was attached a weight P. The other end passed round a small winch T, to which the camera C was connected. Upon the spindle connecting these two parts of the mechanism was a small wing-piece L, one of the extremities of which rested upon a vertical spindle E connected with an electro-magnet F. In the electro-magnet circuit was a small water-balancer B having two cells and a see-saw motion. This was driven by a stream of water flowing from the tap of the tank R. The flow of water from the tap could be regulated.

When the elevated cell of the balancer was filled, its weight caused it to fall. As it fell the electric circuit of the battery V was closed. This caused the small vertical rod E to be drawn downwards by the electro-magnet F. The descent of the rod allowed the leaf L to fall. The make and break in the electro-magnet was instantaneous, so that the vertical rod E immediately returned to its normal position, with the result that, when the wing came round, after completing a revolution, it was stopped, and remained there until the second cell of the water-balancer, filling and falling in its turn, repeated the cycle of operations. As the rod carrying the wing L was the common axis of the winch and the driving mechanism of the camera the release of the wing brought the strain of the weight P upon the cord, and thereby moved the camera driving mechanism a complete revolution. Thus it conformed to the "one-turn-one-picture" movement. It was a combination of weight-driven and electrical mechanism, and, though apparently complicated and certainly cumbersome, it was satisfactory because it completed its work with unerring steadiness and regularity. As the weight P descended a very small distance for each exposure a single winding-up was sufficient to drive the mechanism for several hours. The intervals between the exposures could be varied by turning the tap on or off, thereby changing the volume of water flowing into the balancer. The thinner the water stream the longer the period required to fill the cell, the longer the interval between each see-saw, and obviously the greater the lapse of time between each exposure. Similarly the time intervals between each exposure could be shortened by turning on the tap so that the cell became filled more quickly.

In the Marey Institute investigations with the convolvulus, which was placed on a chair a short distance from the lens of the camera, sixteen successive snap-shots were made in the hour. These pictures, taken at intervals of four minutes, show the complete opening of the flower, the phases in the successive pictures blending so well together as to convey the impression that the pictures were taken at the normal speed.

A striking contrast to the bulky, weighty, and massive apparatus employed ten years ago to photograph intermittently the opening of a flower is the latest device which is employed at this Institute for this work. It is a small, light compact contrivance driven by a kind of carriage clock. This clock actuates two levers whereby electric contacts are made at predetermined intervals to open and close the lens. This mechanism can be set so as to give exposures at intervals ranging from a minute to several hours, and will run for twenty-four hours without attention. The apparatus is as accurate as it is ingenious.

It is obvious, however, in such work, that a great deal depends upon the personality of the worker himself. If he is skilful he will find no difficulty in devising a reliable timing apparatus which he can trust for hours together. But the simpler the character of the appliances the more trustworthy will they prove, because the reduction in the number of the component parts will decrease their liability to derangement and irregular action.

Seeing that exposures have to be continued at the predetermined intervals throughout the whole twenty-four hours, arrangements must be made for artificial illumination during the night. This should not prove a difficult problem. There is a wide range of illuminants—electricity, gas, acetylene, etc.—from which a choice can be made according to the circumstances of the case. Thus a worker living in country districts may find a difficulty in obtaining electric current or coal gas, in which case he must rely upon acetylene, or a petrol gas flame, in conjunction with an incandescent mantle, or even an electric battery and flash-lamp with a reflector.

If electricity or coal gas are available from public supply sources there need be no anxieties whatever. A metallic filament incandescent electric lamp of high power is quite sufficient for the purpose, and if there is need for a concentrated strong light it can be obtained by mounting the lamp within a parabolic reflector, such as is used for automobiles. Coal gas with an incandescent burner and mantle is just as efficient, and concentration in this case can be managed in the same way with a reflector. But it is necessary to make sure that no draughts play upon the gas flame, as the intensity of the light might thus be greatly impoverished.

Acetylene is a very useful and powerful illuminant when all else fails. It is the nearest artificial approach to sunlight. Petrol gas with an incandescent mantle will be found just as good as ordinary coal gas, while there are many cheap lamps well adapted for its use. If all these alternatives are lacking there is the electric flash lamp working with the dry battery. A tiny metallic filament incandescent bulb mounted within a parabolic reflector will give a light of intense brilliancy. But the exhaustion of the battery causes the value of this light to diminish in a relatively short time, so it is well not to let it burn continuously. There should be a means of producing the flash only at the moment the timing apparatus makes the exposure. In one application of this system the flash and the movement of the shutter are controlled by an electro-magnet, arranged in such a manner that the lamp lights up a fraction of a second before the shutter is moved. Thus the object under study is in the full glare of the light before the film is exposed. Of course, if a high capacity accumulator can be obtained, such as that of the latest Edison Nickel type, the light may be left burning continuously. But when there is already an electrical system of actuating the shutter it is a simple matter to incorporate a means of limiting the contact in the lamp to the moment of the exposure.

For the average worker, however, the electrical system is too costly. He will usually prefer a form of light which can be allowed to burn continuously through the night. Even the longest night will not consume a very great quantity of current or gas. Also, unless some very accurate mechanism is used for controlling the intermittent operation of the light, there is always a chance that the exposure and the illumination may fail to synchronise, and thus an excellent film might be ruined.

The "one-turn-one-picture" movement has to be adopted for many subjects other than flowers. For instance, it is necessary in filming the movements of the star-fish, in evolution phenomena such as the emergence of a chicken from its shell, and in the case of certain minute organisms which can be cinematographed only with the aid of a microscope. But the same broad principles apply in each case; there is equal need for time and patience, while complete success can only be achieved by careful observation and ingenuity. There are critical moments in such work and the unexpected frequently happens. Unless the operator is equal to the emergency weeks of tedious labour may be wasted.

The study of exceedingly slow movements offers a very promising field to the patient worker. A film which occupies a month to photograph, and entails an exposure once every thirty minutes, produces a film only 90 feet in length. In projection it passes across the screen in a minute and a half. This means that a process of Nature is condensed into one thirty-seven-thousandth part of the time it actually took, and its presentation on the screen is a remarkable triumph. But at first sight the minute and a half seems a very slight return for the time and labour expended. This is one of the principal reasons why the professional cinematographer displays a marked aversion to the recording of slow movements. On the other hand, it offers unique attractions to the private investigator, for the time occupied in preparing a film that reveals the wonders of Nature invariably commands a high price if it has the elements of popularity or novelty.