PHILOSOPHY OF ZOOLOGY. 



situation, and the mouth and eyes being near the surface of 

 the water, the Jaculator stays a moment quite immoveable, 

 having its eyes directlyfixed on the insect, and then begins to 

 shoot, without ever shewing its mouth above the surface of 

 the water, out of which the single drop shot at the object, 

 seems to rise.* 1 ' No part of the mouth is seen out of the 

 water ; and it shoots a great many drops, one after ano- 

 ther, without leaving its place. Another fish, termed 

 Zeibs insidiator, is known to exhibit the same habits. 

 These errors of refraction thus corrected by the fish, are, 

 perhaps, in a great measure, avoided by birds, and other 

 fishes, by confining their attempts to seize their prey to 

 a perpendicular direction, in which no refraction takes 

 place. 



In examining the colour and direction of objects, the 

 eye is seldom assisted by the other senses ; and the infor- 

 mation which it communicates, is in general correct. But 

 it is otherwise in judging of the magnitude, the distance, 

 or the condition of the surface of bodies. 



We judge of the Magnitude of an object, by the diffe- 

 rent colours whic-h it exhibits, in comparison of the colours 

 of those objects by which it is surrounded. When the 

 same colour pervades the whole, we must remain in doubt, 

 so far as the eye alone is concerned, and even in those cases 

 where there is a great dissimilarity of colour, we are at a 

 loss to determine, whether the difference is produced by the 

 margin of the body itself, or only a portion of its surface. 

 Even after we have determined that the limit of the parti- 

 cular colour marks the boundary of the object, we have still 

 to ascertain the angle which its extreme points form with 

 the eye. But as the size of the angle depends not only 

 upon the real magnitude of the body, but its distance, it 



* Phil. Trans. 1764, p. 89. Tab. ix. ; and 1766, p. 186. 



