26 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [24] 



depths of four or five hundred fathoms, which was another fruitful source 

 of error. 



The accuracy of the thermometer itself and its extreme sensitiveness 

 made it particularly valuable to us where we required several tempera- 

 tures in rapid succession at moderate depths, provided we could control 

 its motions. 



Several devices were tried, and finally a simple gas-pipe, seven-eighths 

 •of an inch inside diameter, was adopted. Several holes were drilled in 

 the end inclosing the bulb, a slit cut in the side to expose the scale, and 

 a pair of slip-hooks held in position by a small spring placed in the 

 opposite end. The thermometer was then inserted; the rubber guards 

 used to protect the shield in the wooden frame serving not only to hold 

 it securely in place but to protect it from sudden jars, and a lanyard ot 

 cod-line, spliced into the end carrying the bulb, completed the arrange- 

 ment. 



THE MESSENGER. 



The messenger used for capsizing the thermometer is of cast brass, 

 cylindrical in form, with rounded ends. It is about two inches in length, 

 one in diameter, and has a three-eighth-inch hole through its center, well 

 rounded at the ends to prevent catching on splices. Its weight is from 

 three to four ounces. 



TO TAKE A DEEP-SEA TEMPERATURE. 



Plate XIII shows both forms of the Negretti & Zambra thermome- 

 ter arranged for descent. In the modified form it is held firmly in 

 position by the slip-hooks through which the stray-line passes. 



Having attained the proper depth, and sufficient time elapsed for the 

 thermometer to indicate the temperature, the messenger, which has 

 been resting in its cradle under the guide-pulley, is sent down the wire 

 and capsizes the thermometer by striking the slip-hooks and forcing 

 them open, when, having lost its support, the instrument promptly 

 reverses, as shown in Plate XIV, Avhere l>oth forms are rei)resented as 

 on the ascent. 



All buoyancy being destroyed by substituting a metal case, the ther- 

 mometer is independent of the motions of the vessel either from rolling, 

 pitching, or drifting. The line may be stopped on the ascent or lowered 

 ugain without affecting the instrument in any way. We have taken 

 hundreds of temperatures with the apparatus described, under varying 

 conditions of wind and weather, with the most satisfactory results. 



THE MILLER-CASELLA DEEP-SEA THERMOMETER, 



Plate XVII shows this thermometer in its copper case used for deep- 

 sea work ; also partially dismounted, to show the form of construction. 

 The magnet seen between the two instruments is used to adjust the 

 indices. 



