THE SCOTTISH MARINE STATIONS AND ITS WORK. 227 



filling c and a portion of the tube above. The scale reads 

 upwards from c. Tlius^ whenever the existing temperatui'e 

 is required it is merely needful to invert the instrument and 

 the reading can be taken at any time afterwards. The left- 

 hand figui'e shows the thermometer enclosed in a stout glass 

 tube to protect it from the pressure of the water at great 

 depths. 



The thermometer is mounted in the " Scottish " deep-sea 

 frame shown in Fig. G. It is swung upon pivots, and the 

 end, c, is loaded so that it will fall down when allowed to 

 do so by the withdrawal of a pin, which fits into a slot at 

 that end. The outer frame carrying this revolving piece is 

 attached to the sounding line by a double hook below and a 

 screw clamp above. The pin, which fits into the slot, is 

 worked by a lever, the other end of which embraces the rope, 

 so that when it is depressed by a " messenger '■* (a weight 

 which slides down the line) the pin is lifted out of the slot, 

 and the thermometer at once turns over. When this has 

 taken place it is held in position by a spring catch fitting 

 into a notch. Lest the thermometer should happen to be so 

 accurately balanced as not to turn over, an india-rubber ring- 

 is fixed to the upper part of the frame so as to give it the 

 required initial impetus. 



The messenger is the invention of Captain Rung, of the 

 Danish Meteorological Institute, and is made in two pieces 

 in such a way that it can be put on the line at any point. 

 When several thermometers are placed on the line at the 

 same time each (except the lowest) has a messenger sus- 

 pended to it, as indicated in the diagram, to cause the 

 inversion of the succeeding thermometer. 



Within the last few months Professor Chrystal has 

 constructed an instrument in which the inversion is accom- 

 plished by electricity, thus doing away with any uncertainty 

 which may attend the action of the messengers and rendering 

 the process instantaneous. The sounding line contains two 

 copper wires which are connected with the terminals of a 

 horse- shoe electro-magnet in the upper part of the frame. 

 As soon as the circuit is completed the pin is drawn out of 

 the slot and the thermometer turns over. The apparatus 



