DEEP-SEA INVESTIGATION. 



65 



Fig. 3. 



eo 



30 



70 



SO 



50 



25 



\c 



20 



/ 



Fig. 4. 



17 



instrument is to be used, the end is closed, and the line let go ; 

 when bottom has been reached it is brought up again, and we find 

 that a certain amount of water has lodged in the 

 lower part of the tube. It is evident that, as the 

 instrument descends and the air in it is compressed, 

 the water forces its way in through an orifice, and 

 past the spout. This spout is so formed that it de- 

 livers the water against the walls of the tube, down 

 which it runs, and collects at the bottom. When 

 the motion of ascent begins, the air, by its elastici- 

 ty, tends to recover its original volume, and ex- 

 pands in the direction of greatest freedom. ISTow, 

 all the water which has entered has collected below 

 the spout ; consequently, in reexpanding, this water 

 will be left undisturbed. 



Assuming that the volume of the mass of air in 

 the instrument varies inversely with the pressure 

 to which it is subjected, we require, in order to be 

 able to construct a scale for our instrument, and so 

 to interpret its results, to know the total volume of 

 the tube, the volume of the part which I call the 

 vestibule, the dimensions and volume of the narrow 

 tube, and of the wide one. 



Fig. 4 represents an instrument modified so that 

 it can be used either for great or small depths, ac- 

 cording as either end is closed. Mr. Hunt, of the 

 United States Coast Survey, has invented an ap- 

 paratus consisting of an air-tight bag, made of 

 flexible material, with a long, flexible tube attached 

 to it. The bag, being filled with air, is sunk to the 

 bottom (in a moderate depth of water), while the 

 other end of the flexible tube is connected with a 

 Bourdon's pressure-gauge in the ship or boat, the 

 observation of which gives an exact profile of the 

 bottom as the bag is towed over it. 



Bottom temperatures may be measured by com- 

 mon thermometers protected so as to be uninflu- 

 enced in coming up through the warmer upper 

 strata of water, by bringing the water to the sur- 

 face and taking its temperature, or by self -register- 

 ing thermometers, such as Cavendish's and Six's. 

 A great amount of ingenuity has been displayed in 

 the invention of machines for registering the ac- 

 tual temperature of the water at any given depth, independently of 

 that of the water above it, all of which require some assistance from 



VOL. XIX. 5 



