178 BULLETIN OF THE 
WORKING. 
The cup comes to the surface filled with water, the screw-cap down on 
the upper valve, and the propeller resting on the cap. To get the water 
out, first screw up the propeller until it takes on the thread of the shaft ; 
then screw up the screw-cap until it uncouples from its thread. The 
valves may then be raised and the water discharged. 
After the screw-cap has been uncoupled the cup is automatic in its 
working, and it is only necessary to clamp it on the line with the spring 
clamp Y. Before paying out the propeller may be screwed up to its 
full extent, but this is not necessary. 
As the cup descends the resistance of the water raises the valves, 
and also screws up the propeller until the lower thread in the hub clears 
the upper thread on the shaft, when the propeller uncouples and revolves 
freely on the shaft, where it is guided at top and bottom, which pre- 
vents chafe on the thread. 
Should a stoppage then be made to fasten on another cup, the pro- 
peller will not screw down by the rolling or pitching of the vessel. | 
It will be noticed that the blades are bent on their upper edge. With 
the blades thus bent, and the propeller made very light, it has been 
found, experimentally, that by rising and falling equal distances through 
the water the propeller will screw up instead of down. Without bending 
the propeller blades, it is evident that the propeller would gradually screw 
down by a rising and falling motion, since its weight would assist its 
screwing down and resist its screwing up; but, even thus, experiments 
have shown that for an alternating motion through the water, continued 
for a longer time than any probable stoppage, the propeller would screw 
down only about a quarter of an inch, which is much within the margin 
of safety ; and, on relowering, the propeller, in that case, would again 
rise and uncouple. . However, the bending of the blades overcomes any 
bad effects from the motion of the vessel, and the valves are free to 
open during the whole descent without regard to the number of stop- 
pages made. 
At any stoppage each cup has within its cylinder a specimen of the 
water from the place where it stops. 
On hauling in, the propeller of each cup screws down, by the resist- 
ance of the water, until the upper thread of the hub clears the lower 
thread of the corresponding screw on the shaft, when the propeller drops 
on the screw-cap, — which until that time has been at rest, — the lugs 
R, R clutch into the slots U, U, and the screw-cap is screwed down until 
it touches the upper valve, which keeps both valves closed. It is evident 
