500 THE DEPTHS OF THE SEA. [CHAP. x. 



the surface. This bottle appeared to answer fairly, 

 and we often had evidence, from its turbidity, that 

 bottom-water came up ; but subsequent experiments 

 have shown that it cannot be depended upon, and 

 some of the reasons are sufficiently obvious. The 

 instrument will not work at all unless the descend- 

 ing motion be sufficiently steady and rapid to main- 

 tain a current capable of keeping two heavy brass 

 valves open to their full extent; if there be the 

 slightest reversal, or jerk, or irregularity in hauling 

 up, the water is at all events partially changed ; 

 the two valves, even when thoroughly open, are 

 directly in the path of the ingress and egress of 

 the water and there is reason to believe that the 

 water is not so rapidly and thoroughly changed as 

 we at first imagined. A perfectly satisfactory water- 

 bottle is still a desideratum, but I believe that one 

 which was used by Dr. Mayer and Dr. Jacobsen 

 in the German North Sea expedition of the past 

 summer, goes far to remedy most of these defects. 

 I hope we may be in a better position to give an 

 opinion a year hence. 



I give, in the appendix to this chapter, an abstract 

 of the general results of the chemical investigations 

 carried on during the ' Porcupine ' cruises of 1869 ; 

 and I add a note, for which I am indebted to my 

 friend Mr. J. Y. Buchanan, who accompanies me as 

 chemist to the ' Challenger ' expedition, which will 

 show how much has yet to be done before we can 

 hope to come to any really satisfactory conclusion 

 as to the amount and condition of the gases con- 

 tained in sea-water. Neither, I regret to say, can 

 we place much reliance on the determination of 



