Reighard. — Senses and Learning in Fishes 155 



but men at a little distance on shore, the lower parts of 

 buildings and the trunks of trees are not visible. Wood 

 (1906), has used a specially constructed pin-hole camera 

 to make photographs which show how the outer world 

 appears to a fish in a pond. With this apparatus he has 

 photographed a circle of nine men as they would appear 

 standing about a small pond with buildings and trees in 

 the background. Although the men are very close to the 

 camera very little of them is visible below the knee and 

 the lower stories of the buildings do not appear in the 

 picture. With a similar apparatus Wood has photo- 

 graphed a straight row of nine men as they appear to a 

 fish in an aquarium when the center man is standing 

 about eighteen inches from the glass side of the aqua- 

 rium. The end men in the row are just included in this 

 picture, so that additional men at either end of the row 

 would be invisible. From the photograph we may esti- 

 mate that the row of men is about 15 ft. long. A line 

 from the outside of the end man iy 2 feet distant, to the 

 center of the side of the aquarium then makes an angle 

 of about 12° with the aquarium glass. Within this angle 

 which corresponds to the line 2 in figure 1, nothing is 

 visible in the photograph. If a six-foot man stands at 

 the edge of a pond with his feet at the water level a line 

 drawn from the top of his head so as to make an angle 

 of 12° with the water surface strikes that surface at a 

 distance of about twenty-five feet. From this very rough 

 calculation it is probable that a six-foot man would be 

 invisible to a fish at a distance of twenty-five feet. As 

 the man comes nearer his head and shoulders become 

 gradually visible and then the rest of his body, but all 

 distorted as already described. From this same calcula- 

 tion it seems that the sun's rays would not penetrate the 

 water appreciably until they formed an angle of 12° with 

 its surface. Hence sunrise comes later for the fish than 

 for us, and sunset earlier and his mid-day is much 

 shortened. 



Von Aufsess found in his experiments with the mirror 

 that all subjects above water were seen surrounded by a 



