146 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
force resulted in no injury to the apparatus. On the ascent the buffer must withstand not only the 
weight of the 50 pounds of metal, but also the resistance which the water offers to the xiassage through 
it of the several jiarts of the apparatus. Moreover, when the cylinder emerges from the water it is 
full of that liquid, aud with this increased weight would overcome the stated resistance of the buffer 
and force the latter downwards until the lead was reached. To meet these conditions it was not 
thought advisable to increase the resistance of the buffer, which would involve a heavier blow against 
the axiparatus, but a roxie-yarn seizing or stop was xdaced on the rox^e about 15 or 20 feet below the 
buffer, beyond which the latter could not x'ass. 
Having secured the buffer to the rope about 5 or 6 fathoms above the lead (a very heavy lead to 
keexi the rope straight) and x>aid out the length of rox>e required to span the stratum to be explored 
by the cylinder, the clainx> and cylinder are attached, the latter being susx^ended from the former as 
follows: Therox^e having been x>laced between the two sliding chocks of the clamxi, the arm of the 
eccentric tumbler is thrown up, which moves the chock M inwards; then, by means of the adjusting 
screw, the chock L is pressed against the roxie, securing the clanqi in xmsition. The cylinder hangs 
4 or 5 inches below the clamp, and is suxJX^orted by a looxi of soft wire which rests on the lixi of the 
tumbler; the ends of the wire, being run through holes in the ux^xier part of the frame of the cylinder, 
are fastened xiernianently to the outer arms of the lever I), to which the valve is screwed. It is seen 
that by this method of susxiension the weight of the cylinder aud its frame is used to keexr the valve 
closed while x>aying out. The cylinder should be tilled with water, xioured down through the ux>per 
sieve, to maintain the valve on its seat while the cylinder is being immersed. Roxre is then imid out 
slowly until the cylinder is at the desired depth, when the rox^e is stoxipered and the messenger sent 
down. The messenger strikes the arm of the eccentric tumbler, throwing it down and tripping the 
cylinder. The tumbler in falling relieves the x^ressure on the sliding chock M, which is then free to 
recede from the roxie. 
Messenger, clamxi, and cylinder fall together, the valve being held oxieu by the resistance of the 
water. A current is established through the cylinder, and specimens which enter are retained by the 
uXixier sieve. When the buffer is reached, the valve is closed by the xiressure against the outer arms 
of the lever. 
A vmry slight xiressure on the adjusting screw of the clamxi, after the chocks are bearing on the 
roxie, is enough to xireveut the clamxi from sliiixiiug, but by an increased xiressure on the screw a greater 
force is required to trixi the tumbler, and by this feature the arm of the tumbler is utilized to break 
the force of the blow which the body of the clamxi receives from the falling messenger. 
A few rings of sheet lead may be laid on the top of the clamxi aud buffer, respectively. 
Nomenclature of Sigsbee’s Gravitating Trap. 
A. Cylinder; coxiper. 
B. Frame; wrought iron. 
D. Lever. 
N. Adjusting screw, 
r. Eccentric tumbler. 
X. Messenger. 
I. I. Looxis, or fairleaders. 
J. J . Rollers. 
K. Frame of friction clamp. 
This aiiparatus was successfully used by Prof. Agassiz on board the Blalce, but 
it did not fulfill all the requirements; the strainers were fine-wire sieves, which were 
somewhat destructive to the more delicate forms, it collected through a vertical area 
when it was desired to exxxlore horizontally, and its limit of action was strictly con- 
fined to the allotted interval on the tow line between the friction-clainji aud the bufter. 
It was the best device of the time, however, aud was duly appreciated by Prof. 
Agassiz. 
THE CHUN-PETEBSEN INTERMEDIATE TOW NET. 
The next apiiaratus to attract attention was the Chun-Petersen tow net, designed 
to collect by towing horizontally at known intermediate depths. A slightly modified 
form of this device was constructed for Prof. Agassiz by D. Ballauf, of Washington, 
D. 0., in 1890, aud sent to the Albatross early in 1891. 
