1911] on Biolotjy and the Cinematograph. 167 



Graphic Method. 



One of the most illustrious names associated with the Royal 

 Institution of Great Britain is that of Thomas Young, who recorded 

 the movements of a vibrating rod on a moving cylinder about the 

 beginning of last century. 



In physiology, however, the foundation of the " Graphic Method " 

 came about in another and quite remarkable way, when Carl Ludwig^ 

 in the small University town of Marburg, on December 12, 1840, 

 recorded on a moving surface the beats of tlie heart as expressed in 

 the variations of the pressure in the arteries coincident with every 

 pulse-beat, and the larger undulations corresponding to every breath — 

 to every rise and fall of the chest-wall. Leaving aside the extra- 

 ordinary development of the graphic method in its application to the 

 arts and in science, let us pass from mechanical methods of recording 

 events to chemical methods, as exemplified by chemically sensitized 

 surfaces exposed in a camera — methods which have rendered the 

 pursuit of cinematography not only useful and attractive, but 

 practical, and practical in the sense of being lucrative. It is only 

 in its infancy as a means for investigating, recording, and solving 

 some of the most obscure phenomena of animal mechanics, which, 

 on account of their rapidity or complexity, have not been solved by 

 other means. 



Luminous Stimuli. 



Whatever may be the exact nature of the events that take place in 

 our visual apparatus when it is stimulated by a luminous stimulus, 

 this we know, that it is excited by slight stimuli, and even by stimuH 

 of exceedingly short duration. A lightning flash, although it lasts 

 only about one-millionth of a second, lasts long enough, not only to 

 stimulate the retina, but to be seen ; and so fleeting is it that a disk 

 or other object moving with great rapidity, when illuminated by an 

 electric spark, appears as if it were stationary. A stimulus of even 

 shorter duration, such as a beam of light reflected from a rotating 

 mirror, will stimulate the visual apparatus though it may last only for 

 one eight-millionth of a second. The visual response is immediate, 

 and there is no latent period that is determinable. An inconceivably 

 brief flash therefore not only affects the retina, but it sets up changes 

 which last for a measurable time. Charpentier has shown that the 

 after-vibrations of the retina occur at about thirty-six per second. If, 

 however, a succession of luminous impressions of the same kind be 

 applied to the retina with sufficient rapidity, they produce the same 

 effect as a continuous illumination. Applying this to the retina itself , 

 then, as Helmholtz puts it, the repetitions of the impressions must be 

 of such rapidity of sequence that the after-effect of the previous im- 

 pression must not have noticeably diminished before the next impres- 

 sion falls on the retina. The persistence of vision applies to coloured 



