THE OTTER-TRAWL. 275 



lightly over the ground, although at the same time closely 

 touching it. We now have the funnel-shaped bag with a 

 long wing of netting extending from each side of the 

 mouth, and the remaining parts to be noticed are the all- 

 important otter-boards by which the wings of the net are 

 kept extended. Most persons are familiar with the 

 principle of flying paper kites, but a few words may be 

 here said on the subject When the kite is thrown up in 

 the air, the wind would of course blow it away if it were 

 not for the string which keeps a strain upon it in an 

 opposite direction ; and if this strain or pull upon it by the 

 string were exactly at the centre of pressure of the wind on 

 the surface of the paper, the kite would either remain 

 steady or sway about in any direction. But if the string be 

 fastened rather more on one side of the centre of pressure 

 of the wind on the kite than on the other, then that part of 

 the kite would be turned a little towards the wind and the 

 rest of it in a corresponding degree away from it. The 

 wind would therefore strike the kite at an angle and with 

 the greatest effect on the part behind the string, tend- 

 ing to blow it away were it not that the pressure of the 

 wind also, although in a less degree, on that part in front of 

 the string, kept it from turning away too much. The kite 

 is thus brought into the same position with respect to the 

 wind as the sail of a vessel is when she is going what is 

 called close to the wind. In both cases the wind strikes at 

 an angle and flies off at the further edge, resulting in the 

 sail and the kite being forced in the opposite direction. 

 The kite, being weighted with the tail, turns its head 

 upwards, and that being the part on which there is the least 

 pressure of the wind, the kite rises in the air. Now if we 

 substitute an otter-board for the kite and water for the 



wind, we shall find precisely the same principle in action. 



T 2 



