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.
[Illustration:
_By courtesy of the Marey Institute._
CONTINUOUS MOVING-PICTURE RECORDS OF THE BEATS AND SOUNDS OF THE
HEART.
Electro-cardiogramme of a normal person. The upper line refers to
the heart beats; the lower line is a photographic record of the
heart sounds. These wonderful pictures are rendered possible by Dr.
Einthoven's string galvanometer in conjunction with Mr. Lucien Bull's
ingenious camera.]
[Illustration:
_By courtesy of the Marey Institute._
CONTINUOUS MOVING-PICTURES OF THE HEART BEATS OF AN EXCITED
PERSON.
The upper line shows the palpitations occurring at irregular intervals,
while the lower line is a cinematographic record of the heart sounds.]
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.
[Illustration:
_By courtesy of the Marey Institute._
CONTINUOUS CINEMATOGRAPHY.--THE PALPITATIONS OF A RABBIT'S
HEART.
The vertical lines indicate the extent of the heart beat, while the
horizontal lines give the time interval.]
[Illustration: THE STEREO-MOTION ORBIT OF A MACHINIST'S HAND.
LINES OF LIGHT INDICATING TO-AND-FRO HAND MOVEMENTS.
The latest development in Micro-motion Study. A small electric
incandescent lamp is attached to the workman's hand, and the lines of
light photographed.]
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.