638 



DEEP-SEA THEKMOMETEaS. 



indices are brought down upon the mercury by passing a magnet along 



the tube." 



Negretti and Zambia's Deep-Sea Thermometer. — It having been urged 

 that the Miller-Casella Thermometer simply registered the coldest tem- 

 perature passed through, without regard to depth, Messrs. Negretti and 

 Zarnbra, scientific instrument makers, devised an apparatus by means of 



which the temperature can be 

 readily ascertained at any depth 

 as required, and if necessary a 

 series of temperatures could be 

 obtained by fixing these Ther- 

 mometers on the sounding-line at 

 such intervals apart as may be 

 determined. Figure 1 represents 

 the Thermometer in the position 

 it occupies during descent, and 

 Fig. 2 as it appears after register- 

 ing. The fan revolves only as 

 the line is drawn up, and attached 

 to it is a screw which permits 

 the Thermometer to turn over in 

 its frame, after the fan has per- 

 formed a certain number of revo- 

 lutions and the column of mer- 

 cury previously above the bulb 

 indicates the precise Temperature 

 at the time of turning over. 



The cylindrical bulb (Fig. 3), 

 containing mercury, has its neck 

 closely contracted at A. When 

 the bulb is downward, it contains 

 sufficient mercury to fill the tube 

 and part of the small reservoir C 

 at the other end of the tube. 

 When the bulb is held upward, 

 the mercury breaks off at A, and 

 fills C and a part of the tube, the 



rtg.l. 



Flff.9. 



Fig. 2. 



mercury indicating the temperature on the scale, as shown in Fig. 3. 

 A simpler form of instrument is constructed for ordinary ship's use. 



Sir William Siemens' Electric Thermometer is a very delicate instrument, 

 by which the Temperature is recorded on deck at any depth desired. We 

 cannot attempt to describe this, it being only suitable for scientific 

 purposes. 



The following illustration has appeared in many previous editions of 

 this work, and, although the instrument is old-fashioned, its principle is 

 good for small depth observations, such as those required by fishermen. 



Captain Livingston says: — "In my thermometric experiments I had 

 several thermometers broken. However, to secure my thermometers 

 from being broken, and to enable me to have a column of water round tha 



