118 



THE VOYAGE OF H.M.S. CHALLENGER. 



has the hole a, into which the eye of the sounding line is spliced. At the lower end it has three 

 notches, b, c, and d. If it is not wished to detach the weight, the sling supporting it is hooked into 

 the notch d, which is considerably below the suspending axis. Consequently, when the tube reaches 

 the bottom and the sounding line above slackens, the tumbler still preserves its upright attitude, and on 

 heaving up, the sinker is recovered along with the tube. If the sinker is not to be recovered, the 

 sling is hooked in the notch b, which is above the axis. When the tube reaches the bottom and the 

 sounding line slackens, the pressure of the sling upsets the tumbler, which falls over into the position 

 tig. 46. In getting into this position the weight drags the sling out of the notch b, and it falls into 

 the notch c. Here it remains as long as the tube is at the bottom, exerting all its weight in pushing 

 it into the ground. On heaving in, the tumbler is drawn into an upright position, when the sling 

 slips free and the tube is brought up without the sinker. When it has been brought to the surface, 



Fig. « 



Fig. 46. 

 Disengaging Apparatus for Buchanan's Water Bottle. 



Fig. 47. 



it is found that the mud tube B is filled with a compact cylinder of mud, which by its weight bas 

 kept the india-rubber valves closed by drawing them tight down on their seats, and has therefore insured 

 that the water enclosed at the bottom has not been contaminated by admixture with other water on 

 the way up. 



The localities, even in mid ocean, where the bottom is " hard ground" are by no means rare, and 

 if the tube just described be dropped on it with a 50 lb. sinker, the mud tube will be much disfigured; 

 but if there be any loose material at all, such as gravel or coral, a little of it will be nearly sure to get 

 entangled behind the comb valve. In the absence, however, of a mud plug, the bottom water will be 

 valueless. As a rule, the bottom of the sea, whether deep or shallow, consists of mud sufficiently soft 

 and tenacious to fill the mud tube throughout the greater part of its length with a compact plug, and if 

 the tube B be screwed water-tight into the lower part of the tube A, it is retained in it just as a liquid 

 is retained in a pipette. In soft mud, clay, Globigerina ooze, and the like, it is better to discard 

 altogether the comb valve L, because it always offers some resistance to the entrance of the mud, and 



