Notes on a Sun-Dial /rem Ivy Church, near Salisbury. 237 



The hour-lines on the east and west faces are inclined to the 

 horizon at an angle of about 50| degrees — this was, therefore, the 

 latitude for which the dial was constructed.' Living myself in 

 this latitude I have had a good opportunity in an unusually sunny 

 spring of noting the movements of the shadows on the various faces. 



The upper face has been used for a horizontal dial. The metallic 

 sub-stile (2 inches in length) is still visible, and many of the Roman 

 numerals indicating the hours, as well as the incisions marking the 

 hour angles, which are fairly accurate for the latitude. The sub- 

 stile is the remains of a triangular gnomon which stood 2*4 inches 

 high with the same inclination to the horizon (50| degrees) as the 

 lines in the east and west faces. In the Dover sun-dial the metallic 

 remains have been regarded (I think erroneously) not as a sub-stile 

 but as the dowels of a cross. Small dials like this would be placed 

 on low pedestals, and the utility of a horizontal dial, as the only one 

 indicating the time from sunrise to sunset, could not be overlooked. 



The south face has an excavated heart with eleven lines in it 

 diverging downwards from above the cusp. This was clearly meant 

 for a south vertical dial, indi6ating the time from 6, a.m., to 6, p.m. 

 But where was the shadow thrown ? Certainly not from the sides, 

 for the boundaries of these shadows would be curvilinear, nor yet 

 from the cusp, for even assuming that this was ever sharp and pointed 

 enough for this purpose, shadow lines would not have been needed, 

 reaching to the bottom. I believe the explanation is to be found 

 in the small slit at the top, the orifice of which points in the direction 

 of the celestial equator. A stilus inserted at right angles in a plug 

 placed in this slit will be inclined 39^ degrees to the face, this being 

 the complement of the latitude, and is the proper indication for the 

 gnomon of a south vertical dial. I must acknowledge, however, 

 that I cannot make the shadows quite tally with the hour-lines. 



^ The sun's apparent daily course is a circle, approximately parallel to the 

 celestial equator. The earth's axis and lines parallel to it are pei-pendiculai" to 

 the equatorial and parallel planes. Shadows, therefore, from obstructions parallel 

 to the earth's axis and so pointing to the celestial pole, are unaltered in lateral 

 direction. A simple geometrical construction shows that the angular height ol 

 the polestar is equal to the latitude. 



