228 



NATURE 



[January 7, i 



CHRONOPHOTOGRAPHV, OR PHOTOGRAPHY 

 AS APPLIED TO MOVING OBJECTS.^ 



THIS subject forms the basis ot a very interesting 

 article, in the Revue Gcm'ralc des Sciences, by Prof. 

 Marey, who explains a new method for the analysis of 

 the movements of various bodies that are under con- 

 sideration, more especially in biological than in physical 

 science. Our readers may remember a book that ap- 

 peared in the year 1882, entitled " The Horse in Motion," 

 published under the auspices of Leland Stanford. Mr. 

 Stanford, wishing to study the relative positions of the 

 feet of horses in rapid motion, employed Mr. Muybridge, 

 who was then noted as a very skilful photographer, to 

 carry out a series of experiments. The success which 

 rewarded their endeavours revealed so much that seemed 

 of importance, that he determined to make a complete 

 study of the subject, and with this intention employed 

 Dr. J. D. B. Stillman, to whom he intrusted the under- 

 taking. 



The method the last mentioned adopted was very 

 similar to that employed later by Mr. Muybridge, the 

 differences being that he only made use of one series of 

 cameras, and that the plates were exposed by the break- 

 ing of threads by the moving object. The revolving 

 disk was also in vogue then, for taking movements of 

 running dogs, flights of bird?, &c., only it was not used 

 to obtain the movements of the horse, as it was found 

 extremely difficult to set the apparatus in motion at the 

 exact moment required, and to regulate it to the speed of 

 the horse. 



It is important, next, to refer to the results obtained by 

 Mr. Muybridge in his later experiments, carried out at 

 the University of Pennsylvania, which were published in 

 a large book containing all the series of photographs. 

 The following is a brief account of the method he used. 



It consisted in the employment of three batteries, each 

 containing twelve cameras. The object of working with 

 three batteries was to enable him to obtain photographs 

 from three points of view simultaneously, and the manner 

 in which he arranged them was as follows. One battery 

 was set parallel to the track along which the object to 

 be photographed moved, so that its image would be 

 formed on each plate successively as it passed before the 

 lenses ; and since the distance between the object and 

 each camera was constant, only one focus was required. 

 Placed at right angles to this track, and directed up and 

 down it, were fixed respectively the two other batteries, 

 and the cameras in these were so adjusted as to have in 

 their field of view the same series of positions as seen in 

 the first battery, only of course from two different stand- 

 points ; but since in this case the distance between the 

 object and the cameras was always varying, each of the 

 latter had to be specially adjusted for its own focus. 



The instantaneous shutters of all the cameras were 

 connected by wires to a set of twelve metal studs situated 

 on the circumference of a disk, each stud being fastened 

 to a set of three wires, each of which comes from the 

 first camera in each battery, the second set from the 

 second cameras, and so on. 



A second disk, placed close by, and carrying a brush, 

 was made to rotate, the brush coming in contact with 

 each of the studs in turn. By this means, a series of 

 currents was sent to these groups of three cameras inter- 

 mittently ; and, as each contact was made, three shutters 

 were simultaneously released — one in each of the series 

 — giving a group of three synchronous pictures of the 

 object that was moving on the track, showing the fore, 

 hind, and lateral views. 



One of the first attempts of Prof. Marey consisted 

 in placing on each foot of the moving animal elastic 

 cushions, which were connected with a chronograph by 



' We are obliged to the editor of the Revue Generate des Sciences for 

 permission to use the illustrations reproduced in this article. 



NO. I I 58, VOL. 45] 



means of flexible tubes. As each foot came in contact 

 with the ground, a record of the impact was obtained, 

 from which interesting results were deduced relating to 

 the peculiarities of the succession of steps, and the time- 

 intervals separating them. 



Having referred above to the earlier experiments, we 

 will now mention the very recent work carried out by 

 him. The method that he here adopts differs consider- 

 ably from his first endeavour, and also from that em- 

 ployed by Muybridge and Stillman. Instead of using 

 many cameras, and therefore many plates, he works with 

 one camera and one plate, and it is on this plate that he 

 produces his scries of photographs. The objects that he 

 wishes to study move in front of a dark background, 

 which is situated directly opposite the camera. Fitted 

 to the camera is a large disk with openings in it, and 

 which is capable of quick or slow rotation in a vertical 

 plane. 



During the passage of one of these openings before the 

 lens, the moving object has its image cast on the photo- 

 graphic plate, and is there recorded : as soon as the 

 aperture has passed, no light can fall on the plate unti 

 the next opening comes opposite. As soon as this arrives, 

 another picture is taken in the same way, but, during the 

 interval that has just elapsed, the object, having changed 

 its place, forms its image naturally on another part of 

 the plate. By continuing this process, one can easily see 

 that, on the plate being developed, a series of successive 

 images will be seen extending from one side to the other. 



With a very slow-moving object, this method cannot 

 be applied so v/ell, unless an intermittent rotation be 

 given to the disk, as we should have a series of overlap- 

 ping images quite undistinguishable from one another. 

 The following illustration (Fig. i) is an example of a 



Fig. I. — Arab horse at full gallop. 



picture obtained by using a continuously revolving disk. 

 Between each exposure it will be seen that the horse has 

 not even travelled its own length, but only a little over 

 half, so that the mingling of all the images results in a 

 picture that is useless for purposes of study. The ques- 

 tion which was raised from such results as shown in the 

 above figure may be formulated thus : How is it possible 

 to reduce the surface of the object, and yet be able to 

 record the movements of its principal members photo- 

 graphically ? The following very artful device, which is 

 shown in the next illustration (Fig. 2), exemplifies the 

 manner in -which Prof. Meyer solved the question. By 

 dressing the object in black, employing a dark back- 

 ground, and placing on the members, the movements ot 

 which he wished to investigate, white lines and spots, he 

 was able to increase the number of exposures per second 

 without introducing overlapping, and to record the suc- 

 cessive positions taken up by them. 



We must mention here that the experiments were only 

 carried out with a man as object ; if a horse had been 

 taken, it would have been necessary to have dressed it in 

 black, and to have put the distinguishing marks on either 

 one of the fore or hind legs, and not on both at once ; 

 otherwise there would have been two complete series of 

 images recorded on one plate at the same time, and over- 

 lapping each other. 



