CHAPTER XI

CONTINUOUS CINEMATOGRAPHIC RECORDS

It has already been pointed out that the intermittent method of taking cinematograph pictures results in the loss of certain motions which occur during the interval when the lens is eclipsed by the shutter. A similar loss is experienced by the eye, in daily life, when it blinks. In the case of blinking, of course, the proportion of movement which escapes observation is exceedingly small. But in cinematography practically one half of the movement is lost. When very rapid movements are being investigated these losses become appreciable--in fact the most vital part of a motion may be missed during the 1/32 part of a second during which the lens is covered by the shutter.

There are many fields in which cinematography as at present practised is quite useless owing to this intermittent eclipse of the lens. Suppose that the behaviour of a rapidly moving piston rod is under observation. With the ordinary type of moving picture camera and process the results are quite misleading. The piston travels so rapidly, perhaps at a rate of 8,000 lineal feet per minute, that with sixteen pictures per second only a very small proportion of the work would be recorded.

This deficiency, however, is remedied by another development in chronophotography. This is the continuous cinematographic record, the outstanding feature of which is the elimination of the revolving shutter and the intermittent movement of the film, in favour of a lens that is constantly open, a sensitized ribbon that moves steadily and continuously all the time the experiment is in progress.

Marey, in the course of his momentous investigations with animated photography, used this system for a number of experiments in which an intermittent exposure would not have afforded sufficiently precise results. Recent experiments have substantiated Marey's contentions upon this point, and have shown how unreliable are the results obtained with sixteen pictures per second where extraordinary precision is required. An effort was made to remove the drawback of the intermittent method by writing in, or divining, the movement which occurred during the periods of eclipse, but this method, in turn, was found to be unreliable. There are some motions which it is impossible to imagine or anticipate, even if they do occur in the one-thirty-second or one-sixty-fourth part of a second.

Under these circumstances the continuous photographing system is now very extensively employed. It has undergone many wonderful developments and achieved extraordinary success.

One of the most interesting and marvellous of its triumphs was won with the extremely sensitive "string" galvanometer, which was invented by the eminent Dutch scientist, Professor Einthoven. This particular apparatus has been of incalculable value to the medical profession, and Monsieur Lucien Bull has constructed a special camera with the idea of obtaining permanent and continuous cinematographic records of the experiments conducted by means of it.

The apparatus employed for this particular sphere of operations is of a somewhat involved character. Fundamentally the camera is that which was designed by Monsieur Bull for photographing the flight of insects at the rate of two thousand pictures per second, but it has been modified to suit the new conditions. The reason why it offers the best chance of securing a continuous record is that its sensitized ribbon is mounted upon a drum, a single winding of which produces a photographic record about 3 feet 6 inches in length.

The principle of the Einthoven string galvanometer may be described roughly in a few words. There is a very fine conducting wire, or fibre, of platinum or silvered quartz, which is stretched across the magnetic field of the galvanometer. It is extremely thin, being virtually a hair. Now, when an electric current, ever so slight, is transmitted through this fibre, or string, as it is called by the inventor, it is deflected from its position of rest, the extent of the deviation varying with the strength of the electrical disturbance. When a slight current is sent through the string it may betray the fact with no more than a slight tremor, but a stronger current will cause it to move violently.

A pencil of light, from an electric arc lamp, is transmitted through the galvanometer in such a way that the string is brilliantly lighted. An enlarged image of the string is then thrown upon the sensitized ribbon in the camera by means of a powerful microscope lens.

Seeing that the time and distance measurements in such delicate experiments as these are of the first importance, the sensitized surface upon which the record is printed--paper or film--is calibrated photographically while the experiment is proceeding. It is divided into small squares, the longitudinal lines referring to the time factor, while the transverse lines indicate the extent of the movement of the quartz thread.

This continuous record system is of inestimable value in connection with physiological researches when details concerning the beating of the heart are desired. A person who places a finger of each hand upon the extremities of the string, witnesses the recording of his own heart beats. For the brief period between each beat the string remains quiescent in its normal position, and the record of the same, the enlarged shadow thrown by the pencil of light through the microscope lens, is made upon the sensitized surface within the camera in the form of a steady straight line. The beat of the heart sends an impulse of electricity through the galvanometer, and causes the string to deviate rapidly. As the pencil of light is shining continuously through the microscope lens of the instrument, it stands to reason that the slightest tremor of the thread, accentuated in the shadow, must be recorded. No vibration is too slight to be caught. Not only is the extent of the vibration photographed and capable of being calculated by means of the calibration, but, as the sensitized ribbon is travelling continuously past the lens, the duration of the vibration is photographed as well.

In the case of a normal and healthy person the number of vibrations on the record, corresponding to heart-beats, will average about 80 per minute, and their extent or amplitude will remain comparatively even. But if the person is in bad health, excited, or exhausted, the palpitations will be depicted in the most erratic manner, both as regards their occurrence and their force. One very powerful palpitation, for instance, may be followed by a comparatively long interval of quiescence, succeeded by several spasmodic short movements at brief unequal periods.

From the medical point of view the perfection of the system offers illimitable opportunities. In the hospital, where a patient may be lying in a critical condition, the surgeon can have a continuous record of the state of his pulse without its being felt by hand at intervals. The physician, in unusual or baffling cases of disease, can have a photographic record of the pulse and heart movements from the moment the symptoms develop until the patient either dies or recovers. It also enables the physician to be informed as to how the invalid is responding to his treatment. Hitherto, the practice has been to feel the pulse at varying specified intervals, to commit the readings to a chart, and then to connect the points by lines so as to show at a glance whether heart movement has accelerated or decelerated, and to what degree. Such charts are satisfactory so far as they go, but they may be erroneous, because the action of the heart may have fluctuated between the readings. With the continuous photographic system, however, guesswork does not enter into the issue at all. The complete story is set down in an unimpeachable graphic manner.

Perhaps the most extraordinary feature of this development is that the very sounds of the heart palpitations can be committed to a sensitized surface in a continuous manner. The principle is much the same as in the case of the record of the heart's movements. There is a small light disk provided with an aperture, mounted upon a stand. Across this aperture is stretched a thread of platinum or quartz. This instrument is placed in the horizontal path of a pencil of light, between the camera and the source of illumination, so that the ray passes through the aperture of the disk to enter the lens of the camera. Consequently the shadow of the quartz thread is thrown upon the sensitized surface in the camera.

A film of soapy water is spread over the aperture in the disk, and this, of course, comes into contact with the quartz thread. The provision of this film in reality converts the disk into a very sensitive diaphragm. Now a stethoscope is placed over the patient's heart, the opposite end of which is connected to the disk in such a way as to bear upon the surface of the soap bubble. When the heart beats the noise which is set up thereby is received by the stethoscope and conveyed to the soap bubble. The bubble, being very sensitive, responds to the sound movement in greater or less degree. As it vibrates, it naturally moves the quartz thread with it, and the moving shadow of the string is caught by the photographic film in the camera.

In this manner the surgeon or observer can have a permanent continuous record of the sound of the heart beats converted into movement, and from the regularity of the oscillations he is able to tell whether the heart is beating regularly. If desired, the record of both the heart-beat as demonstrated by the galvanometer, and the sound of the palpitation as indicated by the soap bubble diaphragm, may be obtained upon one chart, and, in synchrony, so as to set a double check upon the observations.

The chronophotography of continuous movement has been brought to a high stage of perfection by the searching experiments of Professor Einthoven. From the physiological point of view he has contributed most valuable data concerning the heart, for his experiments have been with subjects of all ages and in varying conditions of health. The investigations have been extended to animals also, showing the differences in heart beating phenomena between the various members of the animal kingdom.

There is an increasing tendency to adopt continuous cinematography in preference to the intermittent motion for many other phases of particular study, especially where very fine results are desired. One mechanical engineer has applied the method to the measurement of the deflection of bridges when undergoing tests. Monsieur Deslandres adopted a combination of stylography and chronophotography for recording the vibrations in metal bridges under varying conditions of traffic as far back as 1892, but the direct cinematograph record is to be preferred. Sometimes a camera has been used in combination with the existing processes of observations, so that a photograph of the actual movement and of its extent is obtained simultaneously, while the calibration of the sensitized surface, or the introduction of a clock, like that used by Marey, enables the time intervals to be accurately determined.

Another ingenious form of continuous record, which was made many years ago by Soret and Georges Demeny, the collaborator of Marey, has been revived in an improved form by Mr. Frank B. Gilbreth, the eminent American authority on motion study. In this case a moving film is not absolutely essential, but under certain conditions it is to be preferred. The object of the study is the tracing of motions with a view to their improvement and expedition, or the elimination of unnecessary actions, so that the particular task may be achieved in less time and with reduced exertion.

A stationary plate may be used, and the path of the motion is indicated by a ribbon of light from a small electric incandescent lamp which is attached to the hand or other limb of the subject. In this instance the plate presents an apparent jumble of lines, but by the aid of a magnifying glass the complete cycle of movements can be followed from end to end. When the photographs are taken upon a stationary plate, however, it is necessary that they should be taken stereoscopically, so that relief may be given to the picture to enable the movement to be followed correctly. The hand or limb may not be visible in the photograph, but that is a minor detail, because the path it has described is indicated by the lines of light. When the subject is continually advancing, where it does not double back upon itself, a slowly moving film will supply a complete and perfect graphic record of its progress. But in all such experiments the timing element must be incorporated, or the record will have little practical value, and will provide no conclusive evidence.

A novel application of this method was carried out by Demeny several years ago. The scope of the investigation was the study of the characteristic walks and gaits incidental to certain maladies. Patients suffering from rheumatism and other complaints which interfere with the natural walking motions were taken into a darkened room. Incandescent electric lights were attached to their shoulders, heads, and other parts of their bodies, and these were photographed as the subjects moved about the darkened room. The results upon the sensitized surface were merely the paths described by the moving lights. There have been many applications of the continuous record, especially to the work of testing physical, chemical, or electrical phenomena. The observer is certain to obtain a correct result. This has been shown in certain microscopical observations where the movements are extremely rapid, and where a graphic outline is more important than the photographic detail of the subject.

The great advantage of the continuous cinematographic system is that it records every movement. Even the slightest vibrations will be indicated, and upon a large or small scale according to the rapidity with which the travelling sensitized surface is moved through the camera. Comparative investigation between this and the other systems has proved that the continuous cinematograph shows many motions which the former systems lose. It has introduced the investigator to many curious phenomena of which he was previously ignorant.

One thing must be emphasised. It is the salient difference between the ordinary cinematographic method and the continuously moving film process. The first records upon the film a complete picture of the subject. The second records only the path or trajectory of a _single point_, or at the utmost of a number of points, of the subject under observation. This remark does not refer to the method of cinematographing with the electric spark, which is a totally different and special application of the art.