334 



The second part of the paper was occupied with an examination of 

 the Scottish statutory limit of sea and I'iver, as applicable to the 

 salmon fisheries ; in which the author indicated low-water mark, as 

 the only limit contemplated, and justified the sagacity of our ancient 

 legislators, by proving that, with this limit, the object of the statutes 

 was secured. He pointed out the inapplicability of the physical 

 test which he had previously established, and of the spurious ones 

 which had been noticed, to the settlement of the fishei-y question. He 

 concluded, by expressing his regret, that the Legislature had de- 

 clared certain engines, for catching fish, to be legal or illegal, accord- 

 ing as they are used in sea or river, without defining what is sea or 

 what is river ; and his expectation that, should any bill be brought 

 into Parliament, in connection with this subject, the present state of 

 the law will not be permitted to remain in culpable obscurity. 



3. On the Combined Motions of the Magnetic Needle, and 

 on the Aurora Borealis. By J. A. Broun, Esq. Communi- 

 cated by Sir T. M. Brisbane, Bart. 



When a steel needle or rod is so constructed that its centre of 

 gravity is in a finely-turned axle at right angles to its length, it will 

 rest in any position when the axle is placed upon polished planes ; 

 when, however, we magnetize the needle, it assumes a position which 

 is that of the direction of the magnetic force at the place : in this 

 way we obtain the ordinary dipping-needle. The dipping-needle can 

 obviously move only in one plane, that to which the axle is at right 

 angles ; were it possible to suspend it freely, so that it could move 

 in every plane with evex'y variation of the direction of the magnetic 

 force, we should then be able, by observing the variations of its posi- 

 tion, to determine at once the laws which a magnet in its true posi- 

 tion obeys ; this, however, we have not been able to do ; even the 

 small variations in the vertical plane, which we might expect to ob- 

 tain from the ordinary dipping-needle, are nearly or altogether de- 

 stroyed by the friction of the axle upon its supports ; and there are 

 many mechanical difficulties in the way of the other methods of sus- 

 pension. It has been found convenient, then, to make use of the 

 simplebt methods of suspending magnets in a horizontal plane ; and to 

 endeavour to deduce, from the composition of their motions, the 



