[23] CONSTRUCTION AND WORK OF FIHH-HAWIL 25 



DEEP-SEA THERMOMETERS. 



The Miller-Casella and Negretti & Zambra deep-sea thermometers 

 have been used by the vessels of the Commission. They are both ex- 

 cellent instruments, but the latter possessed some notable advantages 

 for the peculiar service required of them in the prosecution of out- 

 work. 



THE NEGRETTI &: ZAMBRA DEEP SEA THERMOMETER. 



This thermometer is shown in Plate XVI ; the tube removed from itt> 

 ease ; the rubber guards taken oif and laid beside it; the messenger be- 

 tween them. The metal case used by the Commission and the wooden 

 frame furnished by the manufacturers are shown. The spring and slip 

 hooks are removed from the former, and lie beside it. 



The bulb containing the mercury is cylindrical ; the neck much con- 

 tracted, and the tube near it bent in a peculiar manner, with a catch 

 reservoir at the bend. To take the temperature the bulb is held down- 

 ward, when the column of mercury in the tube will be in contact with 

 it- To register the temperature the instrument is capsized ; the column 

 breaking at the bend, falls to the bottom, and the scale is then read in 

 the usual manner, it being marked from the opposite end toward the 

 bulb. 



The tube is completely inclosed in a glass shield, which protects it 

 from pressure, eliminating any errors that might arise from that cause j 

 and in order to avoid sluggishness, the portion surrounding the bulb is 

 filled with mercury. 



This thermometer, as mentioned above, registers by being capsized^ 

 or turned with the bulb up, at the point where the temi^erature is to 

 be taken ; and, to accomplish this, some device is necessary by which 

 the requisite movement will take place with certainty at the proper time> 



For this purpose the manufacturers use a wooden frame containing a 

 charge of shot, which moves freely from end to end, and is of suflicient 

 weight to leave the entire apparatus a slight buoyancy in sea water. 



In using this instrument the end of the frame carrying the bulb is 

 made fast to the sounding-line and is pulled doAvn in the descent; the 

 shot are at the lower end, and the buoyancy of the frame, added to the 

 friction of the water, keeps it in position. 



The ascent is commenced with a quick pull of the line, which, by chang- 

 ing its center of gravity, causes the thermometer to capsize, the weigh'; 

 of shot transferred to the lower end and friction of the water keeping 

 it in position. The ascent should be continuous after it commences, for 

 if the line is stopped or slacked from any cause the thermometer is lia- 

 ble to reverse, giving, of course, erroneous readings. 



We experienced no trouble from this cause in smooth water, but in a 

 sea-way, with the vessels moving rapidly, the results were unsatisfactory ; 

 in fact, totally unreliable. The frames soon became water-logged in 



