Use of Lights in Fisheries. 267 



being able to remove that motive, to offer another, and to entice 

 them into the shallow waters by means of light, whether fixed on 

 the shore, or, as is more plausible, floating where necessary. 



In this there can be no difficulty and little expense ; and if 

 another fact which is here stated is also true, then is there every 

 inducement to the trial ; as the pilchard is at least proved to be 

 attached to light, like all other fishes, if, in this case, it is not 

 absolutely seduced from the shores by it. The asserted fact is, 

 that they are found near the Eddystone light-house, and hot only 

 so, but in shoals directed towards it. Whether this be true or not, 

 the general fact is true ; as, in all cases, light -houses are points of 

 attraction for fish, as effectual as they are for woodcocks. And if 

 it be true that the Eddystone light does seduce the pilchards from 

 their, to us, most profitable road, the problem seems to be solved, 

 and the remedy in the hands of the Cornish philosophers. 



ART. . On the Diagonal Framing of Ships of War, by 

 George Harvey, Esq., F.R. S. 



% 



THE following remarks, on the diagonal framing of Sir Robert 

 Seppings, have been drawn up to assist the young naval engineer 

 in the application of a well-known mechanical principle to the 

 forces operating on the parts of that ingenious system ; the proofs 

 hitherto offered respecting the relative positions of the trusses 

 and ties having been derived from experiment*, or from consi- 

 derations foreign to the legitimate purposes of mechanics. 



The misconceptions that at first existed on this important sub- 

 ject, arose from a mistake of the proper applications of trusses 

 and ties ; the opponents of the proper positions of the ties having 

 omitted to consider the essential principle in constructive car- 

 pentry, that the force which operates to eortend the tie, should at 

 the same time tend to compress the truss. The mechanical lemma 



* See Sir Robert Seppings' paper on the 'Great Strength given to Ships 

 of War by the application of Diagonal Braces,' in the Philosophical Trans- 

 actions for 1818. 



