PREFACE 



The graphic method, with its various developments, 

 has been of immense service to almost every branch 

 of science, and consequently many improvements have 

 of late been effected. Laborious statistics have been 

 replaced by diagrams in which the variations of a 

 curve express in a most striking manner the several 

 phases of a patiently observed phenomenon, and, 

 further, a recording apparatus which works automati- 

 cally can trace the curve of a physical or physiological 

 event, which by reason of its slowness, its feeble- 

 ness, or its rapidity, is otherwise inaccessible to 

 observation. Sometimes, however, a curve which 

 represents the phases of a phenomenon is found so 

 misleading that another and more serviceable method, 

 namely, that of chronophotography, has been invented. 

 The development of these new methods of analyzing 

 movement could never have proceeded within the 

 confined space of a physiological laboratory. For 

 instance, in comparing the locomotion of various 

 species of animals, it is essential that each should 

 be studied under natural conditions : fish in fresh 

 water or marine aquariums ; insects in the open air ; 

 and man, quadrupeds, and birds in wide spaces in 

 which their movements are unfettered. 



