22 



SUBMARINE CABLE LAYING AND REPAIRING. 



subjected. At 2,500 fathoms the pressure amounts to 3 tons 

 per square inch, or about 455 atmospheres, increasing about 

 1 atmosphere for every 5^ fathoms depth. Before protected 



bulbs were introduced break- 



A 



Dl 



SI 



gz 



08 



SB 



» 



"^^ 



Supporting 

 Piece. 



Indiarubber 

 Pacl<ingc 



Thick ' 

 QIass Tube: 



Air-tight 

 Cemented 



Rubber- 

 Partition. 



Mercury 

 Jacket 



due to pressure were 

 frequent, and it was also 

 necessary to apply a correc- 

 tion to eliminate the efifect of 

 pressure on the indications of 

 the instruments. 



Another point of impor- 

 tance is in the taking of serial 

 temperatures with thermo- 

 meters attached to the sound- 

 ing line at diflferent depths. 

 In these observations it is 

 necessary that each thermo- 

 meter shall truly record the 

 temperature at the depth to 

 which it is lowered, and that 

 its indications shall not be 

 afterwards affected by drawing 

 through warmer or coldar 

 water on its way to the sur. 

 face. These conditions have 

 been very satisfactorily met in 

 the capsizing thermometer of 

 Messrs. Negretti and Zamhm. 

 The illustration (Fig. 15) 

 shows the form of the mercury 

 column, bulb and stem, and 

 the manner of enclosing it in 

 a second glass tube to resist 

 sea pressure. For lowering 

 into the sea the thermometer 

 is further protected mechanic- 

 ally by being enclosed in a 

 iDrass tube, as shown at T in Figs. 16 and 17, the tube having 

 an open slot in the centre for reading the indications and 

 several holes below to allow the water to freely circulate round 



T 



Vacuum. 



Thermometer Thermometer in 

 ^ulb and Stem. Protecting Jacket, 



Fig. 15. — Negretti and Zambra's 

 Capsizing Thermometer. 



