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 
