NARRATIVE OF THE CRUISE. 



03 



the contracted point at D, or the outer protecting bulb being filled with mercury instead 



of spirit does not succeed in preserving the inner bulb from pressure, or both these 



causes may be combined. That the outer mercurial bulb does not protect the instrument 



in all cases from pressure appears to be almost certain, as a reference to the table 



shows that the results given by No. 77 at depths of 2775 



and 2530 fathoms are higher than at 700 fathoms, and No. 30 



gives higher readings at 1500 fathoms than at less depths. These 



results could only be obtained if the thermometer bulb were 



influenced by pressure. Nos. 18 and 152 appear to be affected 



both from pressure on the bulb and from pressure closing the 



contracted part of the tube, as at depths less than 400 fathoms 



they agree fairly well with the protected Six instrument, but at 



depths over 400 fathoms their indications are very erratic." 



Since the return of the Challenger, Messrs. Negretti & Zambra 

 have made an important modification in the form of this ther- 

 mometer. The new instrument is not double-limbed, and instead 

 of requiring to describe a complete revolution in order to register 

 the temperature, it requires only to describe half a turn. The 

 construction of the thermometer will be understood by reference 

 to fig. 30. The bulb is cylindrical, and mercury is the ther- 

 mometric 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 

 C is provided. When the bulb is downward it contains sufficient 

 mercury to fill the tube, and a part of the reservoir C, if the 

 temperature be high, leaving sufficient space for the expansion of fio. 30. 

 the mercury. In this position no scale would be possible, as the 

 apparent movement of the mercury would be confined to the 



space C. 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 upwards from C. To set the ther- 

 mometer for observation it is only necessary to place it bulb downward, then the 

 mercury registers the temperature like an ordinary thermometer. Whenever the 

 existing temperature is required, all that has to be done is to turn the thermometer 

 bulb upward, and keep it in this position until read off. The reading may be taken any 

 time after. 



The reversing apparatus at first used with this thermometer was somewhat clumsy and 

 unsatisfactory. It has been replaced by a very elegant instrument, designed by Captain 



* 



-Negretti & Zambra's 

 Improved Standard Deep-Sea 

 Thermometer. 



