104 A STUDY OF SOME 



The Normal Walk. 



In order that the various abnormal gaits slioukl be properly 

 understood, a study of the normal walk had first to be made. In 

 this connection it is hardly necessary to refer to the work of the 

 Weber brothers nor to the earlier results of Marey and Carlet, 

 for they are already the common property of schools and text- 

 books. In more recent years, as is well known, Marey invoked 

 the aid of photography to enable him to confirm and add to his 

 original results obtained by the graphic method. His photo- 

 graphs, however, were confined simply to the analysis of the verti- 

 cal and forward movements of various points of the body, and 

 they gave no information whatever of the direction or extent of 

 the lateral sway. Marey was well aware of this, and by a most 

 ingenious application of the stereoscope to his photographic wheel 

 he endeavored to remedy this defect. The pictures tiiat he ob- 

 tained are exceedingly interesting, and when examined stereoptic- 

 ally give one the impression of an undulating white band extend- 

 ing through space, the undulations being in three directions, 

 forward, vertically, and laterally. His achievement was indeed a 

 brilliant one, and yet the pictures do not admit of a detailed study 

 of the curves. 



However, the method invented by Muybridge, of making simul- 

 taneous serial photographs of a moving man or animal from two 

 points of view at right angles with one another, has yielded pic- 

 tures furnishing all of the elements necessary to determine the 

 various paths of motion. It must, however, be admitted that 

 while by this method the lateral sway is quite definitely ascer- 

 tained, there is a slight loss in the accuracy of the curve of the ver- 

 tical and forward movements, and this arises from several causes. 

 In the first place, a possible and probable source of error is slight 

 irregularity in the intervals of time between the successive photo- 

 graphs of a series. No one would pretend that the same accuracy 

 as regards regularity in the sequence of exposures could obtain in 

 a serial battery of cameras as in such an apparatus as used by 

 Marey, in which the sequence of exposures was determined by the 

 fenestra of a revolving wheel. Notwithstanding, repeated chro- 

 nographic measurements made by Muybridge showed the irregu- 

 larities of these intervals to be exceedingly small even for very 



