Mr. W. G. Horner on the Signs of the Trigonometrical Lines. 87 

 Fig. 1. 



traverse four right angles while the latter traverses two. Also 

 [/3] the point P of the intersection of the revolving lines will 

 describe a circle. For, drop P I perpendicular to A T or its 

 continuation. In either case the z. A C P = 2 I A P ; for it is 

 manifestly indifferent whether these angles are estimated yrcwj 

 the simultaneous outset, or to the simultaneous arrival (a). 



