12 KEPOET OF COMMISSIONER OF FISH AND FISHEEIES. [10] 



balanced upon it. C is a screw -fan attached to a spindle, one end of 

 which works in a socket, D, and on the other end is formed the thread 

 of a screw, E, about half an inch lonj]:, and just above it is a small pin 

 or stop, F, on the spindle. Gr is a sliding stop-piece against which the 

 pin F impinges when the thermometer is adjusted for use. The screw E 

 works into the end of the case B the length of play to which it is adjusted. 

 The number of tnrns of the screw into the case is regulated by means 

 of the pin and stop piece. The thermometer in its case is held in posi- 

 tion by the screw E, and descends into the sea in this position (Fig. 1), 

 the fan C not acting during the descent because it is checked by the 

 stop F. When ascent commences the fan revolves, raises the screw 

 E, and releases the thermometer, which then turns over and registers 

 the temperature of that spot, owing to the axis H being below the center 

 of gravity of the case B, as adjusted for the descent. Each revolution 

 of the fan represents about 10 feet of movement through the water up- 

 ward, so that the whole play of the screw requires 70 or 80 feet ascent ; 

 therefore the space through which the thermometer should pass before 

 turning over must be regulated at starting. If the instrument ascends 

 a few feet by reason of a stoppage of the line while attaching other ther- 

 mometers, or through the heave of the sea, or any cause whatever, the 

 subsequent descent will cause the fan to carry back the stop to its 

 initial position, and such stoppages may occur any number of times pro- 

 vided the line is not made to ascend through the space necessary to 

 cause the fan to release the thermometer. When the hauliug-in has 

 caused the turn over of the thermometer, the lateral spring K forces the 

 spring L into a slot in the case B and clamps it (as seen in Fig. 2) until 

 it is received on board, so that no change of position can occur in the 

 rest of the ascent from any cause. The case B is cut open to expose 

 the scale of the thermometer, and is also perforated to allow the free 

 entry of the water. 



" The construction of the thermometer will be understood by reference 

 to Fig. 3. The bulb is cylindrical, and mercury is the thermometrical 

 fluid. The neck of the bulb is contracted at A, and upon the shape 

 and fineness of this contraction the success of the instrument depends. 

 Beyond A the tube is bent, and a small reservoir is formed at B. At 

 the end of the tube a small receptacle, 0, is provided. When the bulb 

 is downward it contains sufficient mercury to fill the tube, and a part 

 of the reservoir 0, if the temperature is high, leaving sufficient space 

 for the expansion of the mercury. In this position no scale would be 

 possible, as the apparent movement of the mercury would be confined 

 to the space 0. When the thermometer is held bulb upward, the 

 mercury breaks off at A, and by its own weight flows down the tube, 

 filling C, and a portion of the tube above. The scale accordingly is 

 made to read upward from C. To set the thermometer for observation 

 it is only necessary to place it bulb downward, then the mercury takes 

 the temperature just as an ordinary thermometer. Whenever the exist- 



