206 



table.; two l)oats; one sounding machine. The plankton net and sounding appa- 

 ratus and the method of using them may he described here. 



Plankton Net. — An idea of our plankton apparatus and its modus operandi 

 can be gathered from one of the illustrations. The sounding boat was fitted in 

 the stern with a swinging derrick. Through the end of this was attached a 

 pulley, through which the rope supporting the net passed. The derrick was high 

 enough to allow the net to swing clear of the sides of the boat, so that when a 

 haul had been made, the net could ])e swung forward over a tray of tubes, ready 

 to receive the condensed i)lankton. The depth through which hauls were made 

 could be ascertained either by means of the sounding apparatus or by the direct 

 measurement of the plankton rope. The plankton net was built essentially as 

 devised by Ilensen and Apstein, except that the straining net of No. 20 silk bolt- 

 ing cloth, Dufour's, was permanently attached to the truncated cone of canvas. 

 The l)acket which receives the plankton was from necessity greatly simplified, but 

 as no measurements were made with it, and further improvement, both in effi- 

 ciency and simplicity, have been devised, I will describe this instrument as it will 

 be made for next summer. 



The diameter of the bucket will be made one and one-half inches. Its bot- 

 tom will be of a sheet of brass or copper, hammered so that it will be slightly 

 concave or cup-shaped. A hole will be punched from the inside and provided 

 with a nipide soldered on the outside. The sides of the bucket will be made of 

 one piece of wire net of the same caliber as the No. 20 bolting cloth of Dufour.* 

 The upper part of the bucket will consist of a fiat I)rass or copper ring soldered to 

 the wire sides, and j)r()vided with openings through which the binding screws, 

 fastening the whole bucket to the net, may pass. Three legs of narrow strips of cop- 

 per passing from the upper ring along the sides of the bucket, being also fastened to 

 the bottom, will give rigidity to the sides and form a support for the bucket when 

 it is being emptied. To the nipple at the bottom of the bucket will be attached 

 a short rubber tube. The opening in the bottom will be closed with a tight-fitting 

 rubber stopper, manipulated from above by a glass rod passing through its mid- 

 dle. The whole cost of the bucket need not exceed S3.o0. The estimate received 

 on one of Hensen's pattern was $25. 



'■■ Only part of the sides were made of the wire netting during the past summer. A 

 piece of new bolting cloth was found to have 83 per cent, of its surface solid, 17 per cent, 

 being open for the passage of water. The wire cloth used during the past summer had 77 

 per cent, of its surface solid, "23 per cent, being open for the passage of water. Repeated 

 trials of forcing water thick with plankton through the bolting cloth and through the wire 

 .showed that the wire was under such conditions a more eflfective strainer than the cloth. 



