APPENDIX. 127 



It will readily be understood that the accuracy of these analyses 

 upon the uniform tension and strength of the threads con- 

 nected with the springs through which the circuit is formed. The 

 perfection of the pictures depends upon the sensitiveness of the chem- 

 icals and the time occupied in their exposure to light. This time is 

 as nearly instantaneous as can well be conceived. Mr. Muybridge 

 estimates it by comparing the enlargement of the horizontal diameter 

 of an object photographed with the vertical diameter of the same 

 object at one five-thousandth of a second. This can only be deter- 

 mined by measurement, and that approximately even in objects of 

 considerable size ; it is so nearly instantaneous that there is no 

 appreciable loss of proportions from differences between vertical and 

 horizontal diameters. 



University Press: John Wilson & Son, Cambridge. 



