A NEW PRINCIPLE OF AQUICULTURE. 769 



xci and xcii. Pieces of 6 by 6 inch timbers, spliced together if necessary, are bolted 

 together to form a rectangle 19 by 7 5 >< feet. Parallel with the long sides and 

 2)^ feet inside are similar timbers, running the whole length of the raft. This 

 makes an alleyway on each side for the supporting of barrels, and the spaces 

 between the barrels are available for small rearing boxes used in preliminary 

 experiments. Across the inner long timbers are placed 6 by 6 inch beams at 

 intervals of 12 feet, dividing the whole raft into six compartments 12 by 12 

 feet square for the reception of the rearing cars. Except for occasional spaces 

 this completes the lower part of the raft. 



Upon these beams short vertical pieces are set at the corners of the car 

 pools to form a rest for the seven upper crossbeams which run parallel with the 

 lower ones (p. 766, and fig. 3,4, pi. xci) . These upper crossbeams of 4 by 6 inch 

 stock support a loiigitudinal shaft beam, also 4 by 6 inches, which runs the whole 

 length of the float through the middle and upon which are fastened the shaft 

 hangers. 



The two floats on either side of the houseboat are fastened rigidly together 

 with bolted timbers. The inside floats are attached to the houseboat by means 

 of D irons and eyebolts to allow about a foot of up-and-down motion. The 

 floats are built comparatively light and of cheap wood, in view of possible future 

 change of plan as a result of experience. 



Rearing boxes. — The rearing boxes are square, made of Js-inch spruce 

 tongued and grooved boards, nailed to a 2 by 3 inch frame with galvanized 

 nails. The inside dimensions are 10 by 10 by 4 feet. The angles between 

 adjacent sides and between the bottom and sides are truncated by boards 9 

 inches wide and beveled on the edges (fig. 6, pi. xcii; fig. 13, pi. xcvi). The 

 vertical corner frame pieces are left projecting above the top of the box about 2 

 inches, to serve as corner posts for fastening the box in place. Ring bolts are put 

 into the four lower inside corners of the box for use in raising the box for cleaning. 



Window cases 9 by 36 inches are placed on two opposite sides of the box 

 to receive the movable window frames (fig. 6, pi. xcii; fig. 10, pi. xciv). Two 

 similar removable window frames 22 inches square are placed in the bottom 

 about 3 feet from the diagonally opposite corners of the box (fig. 6) . The size 

 of the mesh in these screen windows varies, according to the size of the fry 

 under experiment, from 16 to 2 meshes to the inch. The material is usually 

 woven bronze or copper wire or galvanized "iron." 



In the middle of both sides of the box not having windows a broad slot is 

 cut from the top to within about 8 inches from the bottom. It allows the box 

 to be raised above the water, even though the shaft beam is low (fig. 5, 6, 

 pi. xcii). When the box is down the doors (seen in fig. 9, pi. xciv), which are 

 fastened on the side of the slot referred to, are fastened shut by strong outside 

 buttons. 



