39 



It was at this point that we threw the problem of devising a more ade- 

 quate hi-speed sampler into the hands of John Isaacs. He has developed a hi- 

 speed net which fulfills all of the requirements I have listed above, and for good 

 measure he has developed a depressor for use with the hi-speed nets which has 

 already been found to have many other uses. 



The Isaacs hi-speed sampler is a streamlined tube containing a net and 

 a depth flow meter. Water enters the sampler through a 1" forward opening, is 

 filtered by the net, passes around and activates the meter and is ejected astern. 

 The sampler has been so constructed that it precedes the cable by about a third 

 of its length. The forward end of the sampler is divided so that it may be slid 

 through the cable to an attachment point. It is fastened to the wire by a spheri- 

 cal cable clamp. 



The depth flow meter gives a continuous record on 35 mm. clear acetate 

 film of the depth of the sampler in the water, and the flow of water through it. 

 The principal components of the depth flow meter are (1) an impeller and gear 

 train, (2) a pressure element similar to that used in a bathythermograph with 

 attached stylus, and (3) the recording spool and film. 



One problem faced with all hi-speed gear is how to get the gear to sample 

 at depths below the surface. To get a net down to even moderate depths, such 

 as 20 to 30 meters, requires considerable depressing force. To solve this 

 need, a homogeneous bronze depressor was developed. The depressor was de- 

 signed so that it could be operated at several speeds without changing its charac- 

 teristics. From experience gained on early experinnental models nnade of wood 

 or concrete, it was found essential to construct depressors out of material im- 

 permeable to water, to prevent unbalancing and erratic action by the depressor. 

 An unbalanced depressor can be a very dangerous object, induljging in such er- 

 ratic behavior as flying out of the water and even sailing over the ship. When 

 it again hits the water it is likely as not to dig in with such force as to sever the 

 cable. The bronze depressor has proven to be an exceptionally stable depres- 

 sor. It will be surprising if it is not put to a variety of uses in oceanographic 

 research. 



The Isaacs hi-speed samplers are ordinarily towed at the regular cruis- 

 ing speeds of the oceanographic research vessels on which they are used (8 to 

 12 knots). We have used them in series of 4 nets, spaced to sample at 10, 20, 

 30 and 40 meters actual depth. The samplers obtained an integrated horizontal 

 "strip" sample over the distance hauled, usually about 10 miles. About a cubic 

 meter of water is strained by each net per mile of distance towed. 



The Isaacs hi-speed sampler has as few limitations as any hi-speed 

 sampler yet developed. Since the samplers can be used in series, an integrat- 

 ed picture can be obtained of horizontal and depth distribution in the upper layer. 

 It can be hauled for as long as 8 or 9 hours with one loading of film, although 

 hauls of this length are not made ordinarily. In trial tests, the organisms have 

 come up in good condition after this length of hauling, many still living. This 

 sampler is not as rugged as some samplers, and it has to be treated with care, 

 but this is true of most good oceanographic instruments. This net is described 

 by Isaacs et al (manuscript). 



SAMPLING OF PHYTOPLANKTON AND BACTERIA 



Adequate sampling of the phytoplankton population has always posed 

 problems. How can we obtain an adequate estimate of the standing crop? How 



