238 Notes on a Sun-Dial from the Monaster^/ of 



except, of course at noon, and I am of opinion that the stilus must 

 Lave been in some way bent round the cusp. The excavation 

 answers two purposes, it tends to equalise the hour angles, and its 

 illumination marks Q, a.m., at its beginning and 6^ p.m., at its 

 ending. 



The east face had a short stilus inserted in the central hole. The 

 resemblance of the double plane to an open book standing on the 

 plane of the celestial equator and its side edges and central line, 

 therefore, pointing to the celestial pole, is so generally noticed, that 

 I think it must be intentional. The top of the stilus marks the 

 hours from sunrise to noon, its shadow being on the central polar 

 line at 6, a.m. But it does more than this. Two small metallic 

 marks may be seen at the central point of the outside polar exca- 

 vations. The shadow of the stilus moves at the equinoxes along a 

 line joining these metallic marks, but above it from the autumnal 

 to the vernal equinox, and below it from the vernal to the autumnal ; 

 the maximum divergence being reached at the solstices. One other 

 thing is noticeable : — at 11, a.m., the shadow of the upper plane 

 begins to be thrown on the lower plane — there is, of course, com- 

 plete obscuration over this face at noon. 



The west face has three excavations. A rectangular one with a 

 plane base ; a semi-lenticular one (if I may be allowed this expression 

 to denote the figure obtained by bisecting a thick double-convex 

 lens) ; and a rectangular one with a curved base. The advantage 

 of curved bases in equalising the hour-spaces may be seen by com- 

 paring the first and third of these excavations. In the former (the 

 first) the shadow limit at 1, p.m., is 3 inches from the lower edge : 

 at 2, p.m., it has advanced 7 inches ; and it occupies four hours in 

 passing over the 8 inches which complete the base ; whereas in the 

 latter (the third) the hour lines appear to proceed by regular intervals 

 from 1, p.m., to 8, p.m. (?). This, however, cannot be verified, 

 owing to the damage sustained by the upper or shadow-casting 

 edge. The semi-lenticular excavation was fitted in the centre with 

 a small stilus, indicating the afternoon hours, as the stilus on the 

 east side did the forenoon hours, as well as the period of the year 

 by the line of its movement. Indications of this latter use are 



