646 SEC. 15. GEOGRAPHY. 



3145. Slow-Thermometer, for measuring the temperature of 

 the sea, in ebonite. 



Ministerial Commission for the Scientific Examination of 



the German Seas, at Kiel. 



The Slow Ther>nometer furnishes very accurate readings when it can re- 

 main at moderate depths for an hour. For such cases it is more certain, 

 cheaper, and more durable than registering instruments. 



3 145 a. Apparatus for ascertaining the Temperature of 

 the Sea at various depths. 



J. L. JV. Dictrichson, Christiania, Norway. 



The temperature of the sea at different depths cannot always be ascertained 

 with a maximum and minimum thermometer, because it does not constantly 

 increase or decrease at greater depths. 



Supposing the temperature to be thus: at the surface, 15; at 200 metres, 

 6 ; at 400 metres, 8, it would not be possible to gauge this last temperature 

 with a maximum and minimum thermometer. 



An apparatus must then be used -which shall, in the water and out of the 

 water, preserve the observation taken at the depth. 



The apparatus now submitted supplies this want, and also enables to ascer- 

 tain very easily, by a single immersion, the temperature at different depths. 



The principle is this : 



Two points, and 20, are accurately marked upon a small thermometer tt 

 (Fig. 1) c 8 cm long. 



If its tube be filled at a given point (JT), it will easily break there. A 

 column of mercury, length = xy, will therefore remain in the broken part 

 of the tube. By the outer pressure of the atmosphere, this column will be 

 slightly forced into the tube. If the tube is afterwards exposed to another 

 temperature, the variation resulting therefrom, as affecting the length of the 

 mercury column, will be almost imperceptible. To ascertain the temperature 

 at the time of rupture, it is calculated upon a scale where the distance C, D, is 

 divided into 20 equal parts. Each part, therefore, will indicate the length of 

 a degree. For instance, if it be seen that the point x is placed at ~ 6, and 

 that the length of the column is = 14 parts of the scale, it follows that the 

 temperature at the moment of rupture was = 14 -f- 6 = 8. 



To effect the rupture of the tube at great depths without the registration of 

 the thermometer being affected by the outer pressure, often enormous^ the 

 thermometer is encased within a metal wrapper, as proof as need be, and 

 which can easily be fastened to the lead line by metal wires M and N, shaped 

 corkscrew-wise. 



After fixing the thermometer with a screw (2), the ball upwards, between 

 the two jumelles (V, H), (Fig. 2), the plan of which is seen only from the 

 back, the filing is done at point x, and the top part A, B, of the wrapper is 

 tightly screwed up. The bottom part D forms a kind of hinge, covered over 

 with an india-rubber pipe to prevent the water penetrating into it. 



The apparatus being sunk at the required depth, time is allowed for the 

 thermometer to experience thoroughly the temperature of the surrounding 

 water. A heavy ring is then dropped down the lead line. This ring, follow- 

 ing the apparatus through its entire length, strikes the lever C, F, which 

 swings, and pressing upon the hinge occasions the rupture of the tube by the 

 sharp end E, S, which runs up within the apparatus. 



To prevent the hinge being unduly displaced, it is barred by the screw K, 

 which is removed just as the apparatus is plunged into the water. Likewise, 

 to prevent the tube being broken by any unforeseen shock to the apparatus, 

 it is fixed between two india-rubber strings (V), drawn between the two 

 jumelles which support the thermometer. 



