USE OF INSTANTANEOUS PHOTOGRAPHS 75 



over the back of a bather seated in a sitz bath astonish- 

 ment, dismay, anger, eagerness to escape, and the reaction 

 to shock are all clearly shown. Darwin's studies on " the 

 expression of the emotions " would have been greatly 

 assisted by such analysis, and the subject might even now 

 be developed by the use of serial instantaneous records 

 obtained by photography. It may be useful to those 

 interested in this subject to know that copies of Muybridge's 

 large series of instantaneous photographs* of animal and 

 human subjects in movement are preserved both in the 

 library of the Royal Academy of Arts in London and in 

 the Radcliffe Library at Oxford. I may also mention the 

 extremely valuable series of instantaneous photographs of 

 living bacteria, blood-parasites and infusoria produced by 

 MM. Pathe, and the series of fishes and various invertebrates 

 (including the curious caterpillar-like Peripatus) taken by 

 Mr. Martin Duncan. 



The representation of the moon in pictures of the 

 ordinary size (some three feet long by two in height) is a 

 case in which the artist habitually one may almost say 



* A word is needed in amplification of what was said on p. 53 as to the 

 blending of successive images produced on the retina of the eye by the 

 bioscope or cinematograph or by the old " wheel of life." The point 

 which is of importance is not the length of time during which the stimula- 

 tion of the retina caused by an image endures becoming weaker and 

 weaker as fractions of a second pass but it is this : How long will a 

 stimulus last in undiminished brightness ? How soon must it be followed 

 by another stimulus (another image) so that there may be fusion or con- 

 tinuity, the one succeeding the other before the earlier has had time, not to 

 disappear, but to decline. If it has had time to decline in intensity, the 

 appearance of flickering results. That is what the cinematographer has to 

 avoid. It is found that a quicker succession a shorter interval is neces- 

 sary with strong light than with weaker light in order to produce continuity. 

 With a faint light the interval may be as great as one-tenth of a second ; 

 with a strong light it must not exceed one-thirtieth (or with still stronger 

 light, one-sixtieth) of a second. With the stronger light there is a more 

 rapid and a greater loss of the initial intensity of the impression or effect of 

 stimulus, and though each successive effect remains as long, or longer, in 

 dwindling intensity, you get want of continuity, or " flicker." 



