224 



NATURE 



[January 7, 1892 



A Double Moon. 



On December 22, a well-defined double moon was seen 7m, 

 before^sunrise, which is here now at about 7. The fictitious moon 

 was as a disk of white glass, through which the under-lapping 

 part of the true moon could be seen. Atmospheric conditions 

 being similar next morning, I watched for a repetition of the 

 phenomenon, but after some abortive efforts, consisting of 

 repeated, momentary, ill-defined projections of the moon's shape 

 at a distance of three times the space occupied by her diameter, 

 it was finally "given up." Rose Mary Crawshay. 



Mentone, Hotel du Louvre, December 30, 1891. 



ON THE RELATION OF NATURAL SCIENCE 

 TO ART> 



II. 



■'PHERE is yet another direction in which art owes in- 

 -*- structive disclosures to the progress of photography. 

 In the year 1836, the brothers William and Edward Weber 

 represented, in their celebrated work on the " Mechanism 

 of the Human Locomotive Apparatus," a person in the 

 act of walking, in those attitudes which, according to 

 theoretical calculation, must occur successively during one 

 step. Thence a strange fact became apparent. At the 

 beginning and end of each step, while the body rests for 

 a short time on both feet, the pictures agree perfectly 

 with the ordinary way in which painters have been 

 accustomed to represent walking persons. But during 

 the middle of the step, while one foot is swinging past 

 the other, the effect is highly eccentric, not to say ludi- 

 crous ; the individual appears to be stumbling over his 

 own feet like a tipsy fiddler, and nobody had ever been 

 seen walking in such a way. On the last page of their 

 book, the brothers Weber propose to test the correctness 

 of their diagrammatic figures by the aid of Stampfer and 

 Plateau's stroboscopic disks, in the shape of Horner's 

 Dccdaleum,'- which has, strange to say, returned to us 

 from America as a new invention, under the name of 

 "zoetrope" or even " vivantoscope" ; but whether the 

 proposal was carried out or not, does not appear. 



However, William Weber lived to see his assertions 

 thoroughly justified almost half a century later by in- 

 stantaneous photography. It was first put into practice 

 in 1872 by Mr. Eadweard Muybridge at the suggestion of 

 Mr. Stanford, in order to fix the consecutive attitudes of 

 horses in their different paces. The result was the same 

 as in Weber's diagrammatic figures ; pictures were ob- 

 tained which nobody could believe to have seen in reality. 

 On photographs of street life and processions the camera 

 frequently surprised people in attitudes quite as odd as 

 those attributed to them by the brothers Weber on 

 theoretical grounds. The same is the case with the 

 remarkable series of photographs of a flying bird during 

 one beat of its wings, obtained by M. Marey with his 

 photographic gun. 



The explanation is known to be as follows : An object 

 in motion, the speed of which varies periodically, leaves 

 a deeper and more lasting impression on our mind in 

 those positions which it occupies longest, while the 

 impression is fainter and more fleeting in those through 

 which it passes quickly. Apart from all knowledge of 

 this law, a painter would never represent a Dutch clock 

 in a cottage with the pendulum at the perpendicular, as 

 every spectator would inquire why the clock had been 



' An Address delivered by E. du Bois-Reymond, M.D., F.R.S., at the 

 antiual meeting of the Royal Academy of Sciences of Berlin in commemora- 

 tion of Leibnitz, on July 3, 1890. Translated by his daughter. This Address 

 was first printed in the weekly reports (Sitzungsherichte) of the Berlin 

 Academy, then m Dr. Rodenberg's Deutsche Rundschau, and lastly it was 

 published as a separate pamphlet by Veit and Co., at Leipzig, 1891. Con- 

 linued from p. 204. 



2 Philosophical Magazine, January 1834, 3rd Series, vol. ii., p. 36. 



Stopped. The pendulum, having'swung in one direction, 

 necessarily stops for a moment while preparing to return 

 in the other, and consequently its diverging position is 

 more vividly stamped on our minds than those during 

 which it passes through its position of rest with a maximum 

 of speed. Precisely the same thing occurs with the alter- 

 nately swinging legs of a man during the act of walking ; 

 the body remains longest in the position in which both 

 feet support it, and shortest in that during which one 

 foot swings past the other. We therefore receive scarcely 

 any impression from the latter series of attitudes. We 

 imagine a walking person, and painters accordingly 

 represent him, in the interval between two steps, with both 

 feet touching the ground. 



In the case of a rimning horse, however, particular 

 circumstances intervene. However rapid the succession 

 of instantaneous photographs, we never obtain the usual 

 image of a racing horse such as it appears in large 

 numbers in the print-shops at the racing season, and such 

 as we suppose we actually see in reality. It is different 

 in the case of man ; there among pictures obtained 

 methodically or by chance, which have, so to speak, never 

 been perceived by the naked eye, some will always occur 

 which agree with the usual aspect of a walking person. 

 The difference consists in this, that in a racing horse the 

 interval of time, during which the fore-legs remain in 

 complete extension, does not coincide with that during 

 which the hind-legs are fully extended. Both these posi- 

 tions prevailing in our memory, they are subsequently 

 blended into the traditional picture of a racehorse, whereas 

 instantaneous photography fixes them successively. 

 Consequently the traditional picture is wrong, and 

 exhibits the horse in a position through which it does 

 not even transitorily pass. 



In the year 1882, an illustrated American paper brought 

 out a picture of a steeplechase, in which all the horses are 

 copied from Muybridge's photographs, in attitudes only 

 visible to a rapid plate. This ingenious sketch was com- 

 municated to us by Prof. Eder in Vienna, in a pamphlet 

 on instantaneous photography, and a stranger spectacle 

 cannot well be imagined. The correctness of these 

 apparently wrong pictures can, however, be proved by 

 reahzing the idea originally suggested by the brothers 

 Weber, and integrating into a general impression the 

 periodical motion which has been resolved, as it were, 

 into differential pictures. This is done by gazing in the 

 da^daleum at a series of photographs taken at sufficiently 

 brief intervals from an object in periodical motion, or 

 illuminating or projecting it momentarily during its 

 rapid flight past the eye. The latter method has been 

 put into practice by Mr. Muybridge himself in his 

 " zoopraxiscope," and with us in the electric stroboscope 

 by Mr. Ottomar Anschiitz, a most skilful handler of instan- 

 taneous photography. In both instruments we see men 

 and horses reduced to their natural mode of walking, 

 running, or jumping — with one exception. The speed 

 with which the slits of the dtedaleum pass before the 

 eye, or the period during which each picture is illuminated, 

 being exactly the same for the whole series, the general 

 effect produced is somewhat different from what it would 

 be in real life. On the whole, however, the position 

 in which both feet are touching the ground, prevails, be- 

 cause the motion of the legs slackens when approaching 

 this position, so that the pictures follow each other more 

 closely and almost coincide. 



The series of instantaneous photographs taken by Mr. 

 Muybridge and Mr. Anschiitz from an athlete, during the 

 performance of a muscular effort, are an inexhaustible 

 source of instruction to students of the nude. Mr. 

 Anschiitz's stroboscope exhibits a stone- and a spear- 

 thrower in all the different stages of their violent action : 

 their muscles are seen to swell and slacken, until finally 

 the missile is represented after its discharge, as it cannot 

 move any faster than the hand in the act of hurling it. 



NO. I 15 8, VOL. 45] 



