78 MOVEMENT 



to the joints of the legs, to one of the shoulders, and 

 to the head of the subject. These lamps were con- 

 nected with the battery by means of a carriage, which 

 ran along wire rails, and accommodated itself to the 

 various movements. The negative obtained consisted 

 of a series of bright spots corresponding to the succes- 

 sive positions of the different lamps. By connecting 

 the points by straight lines the geometrical chrono- 

 photograph of the gait was obtained.* 



The combined use of red illumination and the 

 electric light has infinite variations. For instance, 

 if one arranges a powerful electric search-light so that 

 the beams are directed across a room illuminated by 

 red light, only the objects shown up by the electric 

 light will produce a reaction on the photographic 

 plate. 



Colour of Objects and Way of Illuminating them. — 

 When the objects under observation are white, or of 

 some colour that can be photographed, strong illumi- 

 nation is all that is necessary for obtaining good 

 results, because, if the background against which they 

 are projected is quite dark, by slightly prolonging the 

 process of development the images are made to stand 

 out' quite clearly. When, however, the colour of the 

 objects is difficult or impossible to photograph, it is 

 necessary to colour them artificially. 



* As it would be very difficult in this long succession of points to 

 recognize those siniulta ieously formed, the following arrangement 

 was designed: The diaphragm contained live fenestrations, and con- 

 sequently produced five images for every complete revolution. Now, 

 one of these fenestrations was made larger than the rest, and con- 

 sequently the particular image produced by it was of greater intensity 

 than the" others on the plate, owing to the longer exposure. In such 

 a negative one can see that in each series of spots every fifth spot is 

 more accentuated than the intermediate ones. These are the main 

 points which must be connected by straight lines, so as to represent in 

 the diagram the axial position of the limbs at successive moments. 

 As for the little intermediate points, they are not without their use, 

 as by their degree of separation one can measure the rapidity of 

 movement of the vaiious joints. 



