624 REPORT — 1889. 



4. An improved form of Deep-sea Tow-net. By G. C. Bourne, M.A. 



At the last meeting of the British Association Mr. Hoyle exhibited an apparatus 

 for opening and closing a tow-net at any considerable depth below the surface of the 

 water. Ingenious as this device was, it appeared to be defective in one important 

 point — that it depended on the use of the ' traveller,' which is uncertain in its 

 action when any length of line is used, because of the curvature that is necessarily 

 present in a line trailing behind a boat in motion, and also is unsuitable for use 

 with anything but a steel or phosplior-bronze wire rope, and is even untrustworthy 

 when either of these is in use, because it is stopped by any kinks, such as are 

 ■certain to occur in a well-used rope. 



In seeking for a better device for opening and closing a tow-net beneath the 

 water, I was informed of an ingeniou.s instrument invented by Mr. Petersen, the 

 engineer at the Naples Zoological Station ; but this again was defective in con- 

 struction, as the revolving screw, which forms the essential part of his instrument, 

 is liable to become jammed through the strain put upon it by the fastening adopted 

 for the tow-net. 



The instrument which I now describe is a modification and improvement of 

 Petersen's, and was designed for me by Lieut. E. Warre Slade, R.N., to whose 

 design I have added only a few trifling modifications. 



The tow-net is fitted by its mouth to a frame of galvanised iron. This frame 

 consists of two smaller half-hoops, Y (represented as closed in the diagrram), which 

 are hino'ed together so as to form a circular mouth when open. To these the tow- 

 net itself is attached. In addition to these, there is a single and larger half-hoop 

 X. It is obvious that if the tow-net is pulled through the water by the cords G 

 attached to the half-hoop X, the pressure of the water will force apart the two 

 half-hoops Y, and if the cords H attached to the latter are slack, the tow-net will 

 be towed mouth open. 



On the other hand, if G is slacked, and the tow-net is pulled by the cords H 

 attached to each of the half-hoops Y, the tow-net will be pulled along mouth 

 closed. 



So far the arrangement is identical with that adopted both by Mr. Hoyle and 

 Petersen. 



The apparatus for iilternately slackening and pulling upon the cords H and G, 

 so that the tow-net may be closed, opened, and closed again, consists of a brass 

 frame, A A, to the ring at the front end of which the tow-net is made fast. B B is 

 a screw-shaft occupying the centre of the frame, and revolving in bearings at the 

 bottom of the frame and in the cross-piece towards the top of the frame. To the 

 upper end of this screw-shaft the fan C is attached. D is a block through which 

 the screw-shaft passes, and is kept in position by the guides E E. As the guides 

 can only be shown in outline in the figure, a section of the screw-shaft with the 

 guides and block is given on the left hand of the diagram, to show their relations 

 to one another. If the screw-shaft is revolved, the block, being prevented from 

 turning round by the guides, must travel up or down the screw, according as the 

 latter is turned in one direction or the other. At </ ;/ and // are tumbling-hooks 

 and catches, the catches being of such a length that they are lifted by the block 

 D as the latter travels up the screw. The cords G G and F F are fastened to the 

 tumbling-hooks (/ ff and //by rings. The cords G G are fastened to the half-hoop 

 X of the tow-net. The cords F F, when they are fastened in the tumbling-hooks 

 //, pull on the cords H H attached to the half-hoops Y of the tow-net, but when 

 they are freed from the tumbling-hooks the cords J J support the cords H H, and 

 PF lie slack. The lengths of the cords G G and F F (which should be made of 

 wire, to avoid stretching) are so regulated that when both are fixed in their proper 

 tumbling-hooks, the tow-net is supported entirely by F F, but when these are 

 released the tow-net is supported entirely by the cords G G ; J J remaining slack 

 ■until G G are in turn released. 



When the tow-net is required for use the screw is turned round till the block 

 D is at the bottom of the frame, the cords G G, F F, are fastened to their proper 

 tumblin-i--hooks, and the catches of the latter are firmly pressed home. The 



