PHOTOGRAPHY OF AQUATIC ANIMALS. 47 
it is best to use a lens suitable for instantaneous exposure—a lens of a speed not less 
than f 8. The operator should first select the point from which the picture is to 
be taken. He should, of course, have the sun at his back orto one side. If possible 
he should stand on the bank or on some fixed support which extends above the 
surface of the water. From such a position the camera is at a greater height and 
may usually be directed at the surface of the water at an angle of about 45° or 
less from a vertical extending upward from this surface. Rays of light from sub- 
merged objects striking the surface of the water from below at an angle of 48° 35’ 
from a vertical drawn downward (or at a less angle), emerge. They may thus, 
after refraction, reach the camera as indicated by the line wa’ 7’ in figure 1. Rays 
which strike the surface of the water from below at an angle of more than 48° 35’ 
with the vertical are, on the 
other hand, reflected at the 
surface so that they do not 
emerge and enter the camera 
but pass down again into the 
water, as indicated by the 
line « m nin figure 1. 
If the operator is unable 
to find a fixed emergent sup- 
port for the camera he may 
make the exposure while 
standing in the water. The 
camera may then be held in 
the hand or may be supported 
on a tripod which rests on 
the bottom. As the legs of 
the tripod are likely to sink 
into the bottom they should 
be extended to their full 
length. Where the bottom 
is firm an elevated position Fic. 2.—Tripod top by means of which the camera may be inclined at any 
may be obtained for the Piel AOI aT ATCT OMRON A, 
camera by using a tripod with legs some 10 feet long, such as dealers sell for use 
in making pictures of large groups. In such tripods one leg forms a ladder by 
which the camera may be reached. 
The tripod top should consist of two rectangular wooden pieces, as shown in 
figure 2 and in section in figure 1. To the lower piece, which has a large circular 
opening at its center, the legs are attached. The camera is fastened by the tripod 
screw to the upper piece in such a way that one of the legs projects directly backward 
instead of directly forward, as is usual. The two pieces are hinged together at one 
edge, so that they may lie parallel to one another or may be separated like the covers 
of a book until the upper piece forms an angle of 90° with the lower. A rod is 
pivoted by one end to the upper piece at the middle of its free edge, so that it swings 
freely in the vertical plane. This rod passes through a perforated metal block piv- 
oted by one end at the middle of the free edge of the lower piece so as to swing freely 
