404 



INSECTIVOILE. 



or 1953| to 1. Thus an aphis, or any other small insect 

 that can come wholly within the field of vision, will appear 

 very nearly as large to the long-tailed tit as two thousand of 

 the same would do to the human eye. 



As the subject is one of considerable interest, and not 

 generally noticed by authors, it may not be amiss to state 

 the relative magnifying powers, as compared with the human 

 eye, of the eyes of some of the other birds that subsist chiefly 

 by picking their prey from the bark and the buds of trees. 



RELATIVE MAGNIFYING POWERS OF THE HUMAN EYE AND THE 

 EYES OF BIRDS. 



This table will be easily understood. The first column of 

 numbers is the focal length of the eyes in inches and deci- 

 mals, and it is found by actual measurement. The second 

 column is the number of times, and decimals of a time, that 

 the eye of each of the birds, whose names are prefixed, mag- 



