A NEW PRINCIPLE OF AQUICULTURE. 771 



shaft (fig. 21, 22, pi. c). The latter is supported above the shaft beam by adjust- 

 able hangers. All the gears are cast instead of cut and have large teeth (fig. 20, 

 21,22). For our purposes they are probably more satisfactory, and are certainly 

 much cheaper, than cut gears. A nice adjustment is not necessary, and the 

 speed of all the shafting is low, being 36 to 18 revolutions for the horizontal 

 shafts and 9 for that of the propeller. 



The longitudinal driving shaft connects by means of mitered gears to a 

 transverse shaft running back toward the houseboat and engine (diagram, p. 766; 

 fig. 4, pi. xci; fig. 20, pi. xcix). Between this and the transverse shaft of 

 the houseboat is a pair of ball joints of the common type and the peculiar 

 extension device referred to before (fig. 3, pi. xci; fig. 17, pi. xcviii). The lat- 

 ter consists of a sleeve made of two heavy castings fitting loosely over two pieces 

 of square shafting. The two sleeve castings are provided with flanges and are 

 held together by screws, and, to avoid their accidentally slipping off into the 

 water, one end is made fast to the shaft with set screws. Several holes are 

 bored through the sleeve for convenience in oiling. This device allows the 

 square shafting to slide back and forth in the sleeve easily and it has the 

 advantage of being very cheap. It is also very strong, because the shaft has 

 a bearing on the sleeve on all four of its surfaces. 



Shafting, pulleys, and engine on houseboat. — The transverse shaft on the 

 houseboat connects with that on both pairs of side floats in the manner 

 described, and is itself connected with the engine within the house by two 

 sets of ordinary pulleys and belt drives in which the speed of the engine is 

 greatly reduced. Two engines are set up ready to connect with the shaft, so 

 that if either one gives out the other may be used. The engines are 2}4 to 3 

 horsepower Fairbanks-Morse vertical type of gasoline explosion engines, and 

 have proved exceedingly satisfactory. 



Boxes with filters for holding minute larvae. — As a modification of the usual 

 form of box or car, to be used for rearing larvae so small that they would go 

 through any screen with meshes large enough to permit an adequate renewal 

 of water, the following has been adopted: The ordinary boxes are carefully 

 calked in all the seams, and their windows, save one of those in the bottom, 

 are covered with canvas. A gravel and sand filter, made by putting about 4 

 inches of gravel and sand into a shallow box with wooden sides and heavy gal- 

 vanized X'iiich mesh wire in the bottom, is placed over the other bottom win- 

 dow (fig. 31, pi. c). When the car is in place, an old-fashioned bucket chain is 

 rigged on the longitudinal shaft, and the water is thus continually lifted and 

 poured into the hatching box through a short trough. The buckets are painted 

 with asphalt inside and the trough is lined with canvas to prevent contamination 

 of the water from contact with metal or wood. The new water is added, there- 

 fore, at the top of the box gradually — about 3X gallons per minute (fig. 14, 

 pi. xcvi; fig. 15, 16, pi. xcvii). 



