APPABATUS AND APPLIANCES USED. 
49 
to each other by means of a rod on which is a move- 
able float. When lowered to any desired depth, 
both cocks being open to allow the column of water 
to freely pass through, immediately the motion of 
Fig. 6. 
lowering is reversed and hoisting commenced, the 
flat float being pressed on by the weight of water 
above it, shuts both cocks simultaneously, and so 
incloses a specimen of the water at that particular 
depth. 
