CHAP. I. ] THE EQUIPMENT OF THE SHIP. 51 
rangement and dimensions of the parts are sufficiently appar- 
ent from the plate to make further description unnecessary. 
The slipping arrangement is in principle the same as that used 
on Brooke’s sounding-rod. 
In order to adapt this water-bottle to collecting water at in- 
termediate depths, it is fitted with a slipping 
plate, F, Fig. 11, furnished with a metal flap, 
Q, which depresses it when the motion of the 
instrument is reversed. It is inserted into a 
slot, S, immediately below the usual slipping 
plate to which the sounding-line is attached, 
and differs from the latter in having a deeper 
notch, R, and having a slot instead of a hole 
for the reception of the pin T, round which 
it turns. The object of this slot is, that after 
the string has been cast free, the flap may fall 
down close along-side the rod, and afford as 
little resistance as possible in pulling up. In 
using the instrument, it must be let go before 
the flap enters the water, and not checked un- 
til the depth desired has been reached. For 
collecting water at any given depth below the 
surface, and retaining the gases dissolved in it, 
Mr. Buchanan has devised the very ingenious 
instrument (Fig. 12), which, in careful hands, 
gives satisfactory results. It consists of a 
brass tube, A, two inches and a half in diame- 
ter, and of a length suitable to the capacity de- 
sired, closed at both ends by stop-cocks, B, B, 
with #-inch clear passage, attached by flanges, rie.11—tstrament for 
slipping the cylin- 
screwed down upon washers. The stop-cocks ger at intermediate 
are connected by a straight brass beam,C,and,  “°?!™* 
when fully open, the levers D, D, which work them, stand up 
at an angle of 45° to the axis of the instrument, and when fully 
