II20 BULLETIN OF THE BUREAU OF FISHERIES. 



Field glasses. — Field glasses may with great advantage be used where the 

 shyness of the fish precludes a too near approach of the observer. Even prism 

 glasses (stereo-binoculars) may be used, and the writer has found those magnifying 

 about six diameters to be admirable. Field glasses are not only often indispen- 

 sable for viewing fish from a distance, but they are very useful in studying them 

 near at hand, for then they act as magnifiers, by means of which small fish may 

 be very considerably enlarged and the details of larger ones brought out. 



Water glasses. — A very useful form of water glass is that in use on the 

 Florida reefs. It consists of an ordinary wooden pail the bottom of which has 

 been replaced by a circle of ordinary window glass luted into place with hard 

 paraffin. A more convenient form of water glass for many purposes is that 

 designed bv the writer and described in his " Photography of Aquatic Animals " 

 (1908). This is essentially a shallow box of galvanized iron into which there is 

 cemented a bottom of plate glass. The rim of the box has an outwardly pro- 

 jecting lip, which lessens the slopping in of water. A bail of band iron is attached 

 by the ends to the inside of the box in such a way that it can be folded down into 

 the interior when not in use. Stout wires soldered across the corners of the box 

 on the inside serve for the attachment of cords. A cover of galvanized iron fits 

 over the plate glass on the outside and serves to protect it during transportation. 

 The whole device is shown in figure i , plate cxiv, with the cover at the left. This 

 pattern the writer has used in sizes of i , 2, 3, and 4 feet on a side. Under ordinary 

 circumstances the water glass is allowed to float and the observer then has both 

 hands free for taking notes or for using his field glasses. The bail serves as a 

 means of carrying the apparatus about, and in the smaller size fits conveniently 

 over the shoulder, so that the glass may be carried on the back, while the observer 

 wades with both hands free. It serves the further purpose of supporting a shade of 

 black cloth, as shown in figure 2, plate cxiv. A shade of this sort cuts off the 

 light reflected from the sky into the eye of the observer and makes it possible for 

 him to see much more clearly than would otherwise be possible. Where the water 

 is so shallow that the heavy glass would sink so as to strike the bottom or inter- 

 fere with the fish beneath, it may be supported on legs, as shown in figure 2. 

 These legs are rods of iron which run through thimbles at the corners of the 

 box and may be set at any height and held in place by thumb screws. The figure 

 shows an observer studying the habits of the brook lamprey by the aid of such 

 a water glass. The lampreys {Lampctra wildcri) were engaged in nest building 

 and spawning beneath the glass and were not only studied but photographed 

 by its help. 



Of the various sizes of this type of water glass, that of i foot square is most 

 convenient for ordinary field work where it must be carried from place to place 

 by the observer, but this size is too small for photographic work. For this 

 purpose the 2-foot glass shown in figure 2 is better adapted and is still not too 

 burdensome to be carried by hand. The larger sizes are suitable only for 



