36 John Graitan : 



HH. — Two screws, passing through the extremities of E and G, 

 constituting the axis upon which G revolves, in a plane 

 always perpendicular to the plane of rotation of E. The 

 inner ends of these screws terminate in smooth cylindrical 

 pivots, of suitable dimensions, to permit of their being 

 introduced into the external auditory foramina. They can 

 be screwed backwards or forwards with the utmost facility ; 

 and when adjusted to a skull, are fixed in a postion by 

 means of the nuts II. 

 II. — Binding nuts, for fixing the stage G firmly to the screws 

 HH, in order that they may rotate with it in its progress. 



J. — A brass semicircle, divided into degress, and firmly secured 

 by screws upon the upper arm of E. Its centre coincides 

 with the axis of G, and it is traversed by an index K, 

 secured upon H by the binding-nut L, so as to insure its 

 accompanying H and G in all their movements, the ex. 

 tent of which can thus be read off in degrees. 



K. — The Index attached to the screw H. When E stands in 

 the position in which it is placed in the diagram, the faces 

 of J and K lie horizontally, and consequently only their 

 edges can be seen ; but a detached diagram of them is set 

 out separately. 



L. — A binding-nut, for fixing the index K in position when 

 adjusted. 



M. — A piece of whalebone 3^ inches long, i}4 broad, and 

 2-ioths thick, securely, but slackly attached by twine to the 

 upper surface of the short projecting arm of G, so as to 

 allow it a sort of hinge-like motion. It is imperfectly 

 visible in position in the diagram, but a detached outline 

 of it is given ; two dots upon it, and upon G, respectively, 

 indicating the holes by which they, are secured to each 

 other. 



N. — A thumb-screw passing through G, and pressing against the 

 back of M, by means of which the distance of M from G, 

 and the pressure exerted upon M can be regulated. 



