THE SEA FISHERIES OF EASTERN NORTH AMERICA. 153 



This treaty is referred to in the Report of the British Sea Fisheries 

 Commission, where it is expressly stated that the vessels of Belgium, 

 with which there was no such treaty, were not bound by it, and that 

 there was nothing to prevent their fishing if they were so minded, in- 

 dicating that the submission to a restriction must be a matter of joint 

 agreement between two contracting parties (p. lxiv). 



With reference to the difficulty of estimating the extent of the three- 

 mile limit, Prof. George F. Barker, writing from Brookfield Center, 

 Conn., September 7, 1877, said: 



" With reference to the question you propose, i. e., whether the proba- 

 bility of an accurate judgment of distance is greater when the estimate 

 is made by an observer standing on shore or by a person in the vessel, 

 I would say that in my opinion the probability of a correct estimate of 

 distance is considerably greater in the latter case. Distance, according 

 to the present theory of vision, is always estimated by the eye from the 

 magnitude of the visual angle under which the distant object is seen. 

 Now, since any given object, placed at a suitable distance, will subtend 

 any angle whatever, it is obvious that size and distance are both vari- 

 ables in the calculation, aud that if neither is given the problem is in- 

 determinate. A man who does not know how large the object is which 

 he sees, cannot, from tbis datum alone, form any accurate idea of its 

 distance. Hence, to estimate the distance of any object accurately, the 

 size of the object which subtends the given visual angle must be accu- 

 rately known. A man of average height placed a mile off will subtend 

 an angle of about two minutes, and if two miles off, of about one minute. 

 To tell that he is two miles off, and not one mile, the eye must accu- 

 rately appreciate this slight difference of one minute of arc. The hu- 

 man height is so well known that persons are often introduced into art 

 compositions to assist in judging of distances. But at three miles dis- 

 tance, a man is too small an object by which to estimate distance by 

 the unaided eye, the limit of error being so large as to render the esti- 

 mate of no value. Hence, other familiar objects larger in size must be 

 chosen. If a person on the shore, accustomed to this kind of estimate, 

 sees a vessel which he is familiar with at the landing, he can tell ap- 

 proximately her distance, if she is not too far off. So a person sailing 

 away from the shore may estimate quite accurately his distance from 

 it, provided he be familiar with the size of the objects on shore. If 

 neither person knows bj r personal inspection the size of the object looked 

 at, the one in the vessel has the advantage, because the sizes of houses 

 'and their parts, windows, doors, &c, and also of well-known trees and 

 animals, vary much less than the sizes of vessels. But there is another 

 advantage on the side of the man in the vessel. He forms his judg- 

 ment not by a comparison with a single object, but from a large num- 

 ber of objects, whose sizes are well known ; and his estimate is, therefore, 

 the mean of a large number of separate judgments, and so more reliable 

 than any single one. Moreover, if these objects are successively back 



