196 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 directly fixed 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.*” No part of the moutlris seen out of the 
water; and it shoots a great many drops, one after ano- 
ther, without leaving its place. Another fish, termed 
Zeus 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 mfor- 
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 which it exhibits, in comparison of the cclours 
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 
raargin 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. 
