262 



PHYSIOGRAPHY. 



[chap. 



line on reaching the bottom. The sounding-line thus runs 

 down carrying a weight, but comes up free, bringing only a 

 sample of the bottom, which is collected on the floor of the 

 sea in a cup, or a tube, or a scoop. 



Without referring to the various modifications of sounding 

 apparatus which have been employed by successive deep-sea 

 expeditions,^ it will be sufficient to describe the sounding 

 machine which was very largely used, during the recent 



voyage of the Challengej: This 

 is represented in Fig. 76, and a 

 section is given in Fig. 77. The 

 apparatus is a modification of one 

 which had been used by Captain 

 Shortland in H.M.S. Hydra, 

 whence it is sometimes called 

 the " Hydra Machine ; " its pre- 

 sent form, however, is due to 

 Lieutenant Baillie. 



This apparatus consists of a 

 metal tube a, mostly of iron, five 

 and-a-half feet in length, and two 

 and-a-half inches in diameter. 

 Its upper end is furnished with 

 a brass cylinder, b, in which a 

 heavy piece of iron works up 

 and down, like a piston in a cylin- 

 der. At c, this iron is furnished 

 with a shoulder, which carries the iron-wire sling to which 

 the sinking-weights are attached. These sinkers, d, are made 

 of iron, cast in the form of cylinders, each with a central hole; 

 they are provided with teeth and notches, so as to fit one 



^ Descriptions and figures of these instruments will be found in The 

 Depths of the Sea, by C. Wyville Thomson, LL.D., &c. 1873. 



Fig. 76, 



Fig. 



Deep-sea sounding apparatus used 

 by ihe Challenger. 



