158 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



the lead (a very heavy lead to keep the steel rope straight) and payed 

 out the length of rope required to span the stratum to be explored by the 

 cylinder, the clamp and cylinder are attached, the latter being suspended 

 from the former as follows. The rope having been placed between the 

 two sliding chocks of the clamp, the arm of the eccentric tumbler is 

 thrown np, which moves the chock M inwards ; then, by means of the 

 adjusting screw^, the chock L is pressed against the rope, securing the 

 clamp in position. The cylinder hangs four or five inches below the 

 clamp and is supported by a loop of soft wire which rests on the lip of 

 the tumbler; tlie ends of the wire, being rove through holes in the upper 

 part of the frame of the cylinder, are fastened permanently to the outer 

 arms of the lever to which the valve is screwed. It is seen that by this 

 method of suspension the weight of the cylinder and its frame is used to 

 keep the valve closed while paying out.'"^ The cylinder should be filled 

 with water, poured down through the upper sieve, to maintain the valve 

 on its seat while the cylinder is being immersed. Rope is then payed 

 out slowly until the cylinder is at the desired depth, w^hen the rope is 

 stoppered, and the messenger sent down. 



The messenger strikes the arm of the eccentric tumbler, throwing it 

 down and tripping the cylinder. The tumbler in fa,lling relieves the 

 pressure on the sliding chock M, which is then free to recede from the 

 rope. Messenger, clamp, and cylinder fall together, the valve being held 

 open by the resistance of the water. A current is established through 

 the cylinder, and specimens which enter are retained by the upper sieve. 

 When the buffer is reached, the valve is closed by the pressure against 

 the outer arms of the lever. 



A very slight pressure on the adjusting screw of the clamp, after the 

 chocks are bearing against the rope, is enough to jjrevent the clamp 

 from slipping, but by an increased pressure on the screw a greater force 

 is required to trip the tumbler, and by this feature the arm of the tum- 

 bler is utilized to break the force of the blov/ which the body of the 

 clamp receives from the falling messenger. A few rings of sheet-lead 

 may be laid on top of the clamp and the buffer respectively. 



"Washington, D. C, September, 1880. 



* It is suggested that, in lieu of the soft wire sling, the friction clamp be constructed 

 to receive the end of a stiff wire rod, proceeding from the ends of the lever D D, and 

 that it be done in such a way that, when the valve is closed and the rod connected 

 with the clamp, the bottom of the latter will be in firm contact with the upper part of 

 the cylinder frame. Such an arrangement would effectually guard against the open- 

 ing of the valve with any rapidity of descent. 



