104' Royal Irish Jcadcmj/. 



The numbers in column (3) being almost exactly the integers, 4, 2, 

 1, and 26, show that the substance analysed is a true alumn, having, 

 as respects its acid and bases, the same formula 



(0SO3, AL O3 + SO3, MnO + 26HO) 

 with all the known species of that genus, and the same number of 

 atoms of water with soda alumn. It differs from all those previously 

 known in containing no alkali, this being replaced by protoxide of 

 manganese. As an additional peculiarity Dr. A. observed that it did 

 not appear susceptible of assuming the octohedral lorm. 



The paper concluded with some remarks upon the probable exist- 

 ence of an alumn containing no metal but manganese, and upon 

 certain difficulties in the doctrines of isomorphism, suggested by 

 some of the varieties of this class of salts. 



Captain Portlock brought under the notice of the Academy some 

 peculiar habits of the Otus Brachyotos or short-eared owl, lately ob- 

 served by Captain Neely, whilst collecting for the Ordnance Survey 

 of Ireland. 



This species of the sub-genus Otus being migratory, is much rarer 

 than the Otus vulgaris or long-eared owl, and it differs from it in many 

 striking respects, such as the small size of the elongated feathers, 

 commonly called ears, (which in this species can only be discerned 

 when the bird is living,) and in its tendency to diurnal habits. But 

 in the instance now recorded it exhibits other peculiarities of habit 

 which afford a still more remarkable line of distinction. The point 

 of Magilligan, forming the Derry side of the opening of Lough Foyle 

 to the sea, is studded at its extremity with numerous sand hillocks, 

 in which the rabbits burrow and the sheldrakes lay their eggs, as in 

 other similar localities. But here a new occupant for the burrows 

 of the rabbits appears in the Otus brachyotos. These birds are regular 

 their autumnal appearance, and are seen to sit at the openings of the 

 burrow-holes, and to run into them when disturbed. 



Captain Portlock having directed further attention to the fact, and 

 pointed out the necessity of guarding against any source of fallacy, 

 the truth of the first statement was fully established, more than one 

 having been shot on emerging from the holes, and another actually 

 caught in a trap at the mouth of a hole when endeavouring to make 

 his escape, 'i'his interesting fact naturally recalls to recollection the 

 Striv cunicularia of America, described by Say ; and Captain Port- 

 lock pointed out the great value of characteristic traits of habit in 

 elucidating classification, and suggested the peculiar importance of 

 those described in his paper, in affording a link of resemblance be- 

 tween the Strix cunicularia and the Otus brachyotos, and thereby faci- 

 litating the determination of the true place, in natural classification, 

 of the former, hitherto considered doubtful. 



The Secretary communicated the substance of a paper " On the 

 Conic Sections ■" by James Booth, Esq. 



The methods hitherto adopted in deducing the central and focal 

 properties of the conic sections, from arbitrary definitions, having 

 appeared to the author defective in geometrical elegance, he has en- 

 deavoured in this paper to derive them from new definitions, of which 

 the following may be considered the principal : 



