The sampler is equipped with a shutter; 

 this is opened or closed by means of a spe- 

 cially shaped messenger which travels along 

 the wire to which the sampler is attached. 

 When the shutter is in the open position, water 

 passes through the flow meter causing the 

 impeller to spin and on through the net thus 

 filtering out zooplankton and phytoplankton. 

 The impeller stops spinning when the shutter is 

 closed by a second messenger. Thus, a sample 

 can be taken at a desired depth by means of 

 this sampler without contamination from plank- 

 ton in the overlying water strata. 



The Clarke-Bumpus sampler is therefore 

 unique in that an uncontaminated sample can 

 be taken from any desired depth, and an esti- 

 mate of the filtered volume of sea water can be 

 determined. 



This sampler was designed to be towed 

 horizontally from a wire kept as nearly vertical 

 as possible by means of a weight attached to 

 the lower end. The weight should be as heavy 

 as is feasible. Weights from 100 to 150 pounds 

 are suitable for large vessels such as the survey 

 ships of the Hydrographic Office, but lighter 

 weights can be used when working from small 

 boats. 



When towing this sampler, a vessel can 

 travel at 0.5 to 3 knots, preferably between 1 

 and 2 knots. Moreover, it can be used when 

 a ship is stopped and drifting at 0.5 knot or 

 faster. If a ship is at anchor, however, cur- 

 rents of 0.5 knot or more must be present 

 in order to get a reading on the meter. Should 

 currents be less than 0.5 knot, a vertical tow 

 can be made with the meter traveling at this 

 minimum speed. If the investigator desires a 

 plankton sample at a specific depth under these 

 conditions, he can obtain it with the Clarke- 

 Bumpus sampler; however, it would not be a 

 quantitative sample since there would be no 

 way to measure the volume of water filtered. 



The instrument consists essentially of a brass 

 tube, 5 inches in diameter and 6 inches long. 

 To the rear end of this, any one of a set of inter- 

 changeable nets, of any desired mesh which 

 are approximately 2 feet long, may be secured 

 by means of a ring with a bayonet lock. The 

 tube is mounted on the frame and this is 

 attached directly to the supporting wire. The 

 frame attaches to the wire by means of a loosely 

 fitting spring pin at the top and a gate lock at 

 the bottom. The latter closes around the neck 

 of the supporting clamp which is secured rigidly 

 to the wire. Thus, the frame is allowed to 

 swivel freely around the wire, and the opening 

 of the tube is always directed forward when the 

 ship is moving ahead. 



The shutter at the front end of the tube con- 

 sists of a disk mounted on vertical pivots. 

 Special messengers open the shutter when the 

 sampler is at the desired depth and close it 

 before hauling begins. 



An impeller is mounted within the rear half 

 of the tube. This is geared to a cyclometer- 

 type counter which indicates the number of 

 revolutions of the impeller and, thus, the vol- 

 ume of water which has passed through the 

 tube and net. The meter starts when the 

 shutter opens and stops when it closes. The 

 bucket is attached to the cod end of the net by 

 means of a throw clamp. The bucket is pro- 

 vided with a draining window covered by fine 

 wire netting. The mesh of the wire netting 

 in the draining cup must be at least as fine as 

 that of the silk netting used. The mesh of the 

 silk netting may be as fine as No. 10 (109 

 threads per inch) but with this and finer meshes, 

 the meter will not record accurately if excessive 

 clogging of the net occiu-s. 



8-12 Assembly of the Clarke-Bumpus 

 Sampler. — The sampler is delivered by the 

 manufacturer already assembled except for 

 the net, bucket, and towing rod. When pre- 

 paring to make an observation, the net is 

 attached to the sampler by means of a bayonet 

 lock. The plankton bucket with the same mesh 

 is then fastened to the cod end of the net with 

 a throw clamp. Next, the towing rod must be 

 installed. This keeps the net open and prevents 

 it from getting fouled on the instrument or 

 cable. The forward end of the rod passes 

 through a guide at the upper rear edge of the 

 main tube and is clamped to the bucket. The 

 sampler is now ready for a plankton observation. 



8-13 How to Operate the Net.— It is best 

 to set the shutter of the sampler before the 

 instrument is attached to the cable. Start 

 with the shutter in the final closed position. 

 Now rotate the shutter through 90° against 

 its spring (counterclockwise looking down on 

 sampler) and at the same time rotate rod (A) 

 clockwise against its spring (2) until the edge 

 of the shutter engages the longer of the two 

 finger lugs (B) (fig. 8.2). At this point, the 

 first of the short horizontal arms (C) mounted 

 in the cap at the top of the rod (A) should 

 engage with the rod (D) extending down- 

 ward from the trigger (E). If the position of 

 this arm is not exactly correct, adjust it by 

 means of the set screw in the cap. Then the 

 shutter must rotate through a second arc of 

 90°, also counterclockwise, and at the same 

 time rotate rod (A), clockwise as before, until 

 the semicircular rod attached to the shutter 

 engages the shorter of the finger lugs (B) and 



80 



H. O. 607 



