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Mr. PETRIE'S Inquiry into the Origin and 



nine inches in thickness. The interior exhibits rests for four stories, including 

 that on a level with the doorway, and beneath which there was a fifth story, not 

 lighted. The second and third stories are each lighted by a single quadrangular 

 aperture ; and the upper story, as in the Tower of Tullaherin, contains eight 

 openings of the same form. The doorway is five feet three inches in height, 

 two feet three inches in width, immediately under the imposts, and two feet six 

 inches, at the sill. The key-stone, and those forming the imposts, extend the 

 entire thickness of the wall, as does the sill-stone also, which is five feet in length. 

 I have now to notice the peculiarities of the upper apertures of the Towers. 

 The apertures in the uppermost story are almost invariably of larger size than 

 those in the lower stories, including even the doorways. The apertures in the 

 intermediate stories, between the uppermost and the doorway, are usually of very 

 small size. In many of the Towers, however, an aperture placed in one of those 

 intermediate stories directly over the doorway, is, as I have already remarked, 

 little, or not at all inferior in size to the doorway. In the external forms of 



these apertures there are but three varieties, namely, the quadrangular, the 

 semicircular-headed, and the angular-headed; and the jambs, in all cases, incline : 

 but, in their internal construction, they present several varieties, which I shall 

 presently notice. As an example of a horizontal-headed aperture, I have given, 



