A UNIQUE SUNDIAL. 



Bv O. PAUL MONCKTOX. 



SixcE the davs of Ahab, King of Israel, the art of 

 dialHng has been practised by kings and princes as 

 well as h\ less favoured folk : but although many 

 quaint dials are known to be in existence, the writer 

 quite recently came across a specimen which must 

 be unique in the annals of horology. 



This dial, of which a full-size 

 drawing will be seen in Figure 

 1, 2, and 3, consists of a short 

 c\lindrical body, made of wood 

 two-and-a-half inches long by 



Figure 1 



The cylinder. The 



dotted Hue shows 



the hollowed 



recess. 



Figure 2. 



The cylinder cap with 



the gnomon lying in 



the saw cut. 



plate is underneath and projects at right angles to 

 the c\linder. The long edge of the gnomon, resting 

 on the flat top of the c\linder, is thus compelled to 

 assume a horizontal position w hen the cap is pressed 

 home as in Figure 3. 



When not in use, the gnomon is twisted through 

 a right angle and rests in the saw cut. Thus the 

 dial can easily be carried in the pocket. 



The vertical lines drawn down the cylinder corres- 

 pond to the months of the year, the letters of the 

 alphabet indicating the different months — D. for 

 December, and so on. 



Referring now to the developed cylindri- 

 cal surface, in Figure 4, the vertical lines 

 correspond to the lines on the cylinder, the 

 letters at the bottoms to the months in the 

 year, and the point marks on certain of 

 the verticals, to calculated inter- 

 vals measuring from the top of the 

 c\ linder. These intervals depend 

 in length on the latitude of the 

 place for which the sundial is 

 designed, the time of day, and the 

 particular length of gnomon taken — in this 

 case three-quarters of an inch. 



The vertical numbers, one, two, three, 

 four, and so on, refer to the hours of the 

 da\'. The cross-curves, drawn in red ink 

 on the original cylinder, join up corres- 

 ponding points on different verticals. -As 



^B 



\ 



arrow indicates the 

 pivot on which it turns, 

 the lower arrow shows 

 the direction of the 

 shadow vertically down 

 the cvlinder. 



three-quarters of an inch in diameter, 

 surmounted b\- a wooden conical cap 

 one-and-a-half inches long b}- three- 

 quarters of an inch in diameter at its 1 igure 3. 

 thickest section. This cap fits into the This shows the gnomon 

 top of the c^•linder. the latter being in position. The upper 

 made hollow for the [)urpose. 



The whole of the dial-cap and 

 cylinder, with the e.xception of the 

 gnomon, was made of a light vellow 

 wood. Vertical lines are scribed at 

 intervals down the whol'_ length of 

 the cylinder ; Figure 4 show s the development of 

 these lines as if the surface of the cylinder were 

 laid flat on a piece of paper. 



The shank CD of the cap fits into the hollow .\B 

 down the centre of the cslinder. .\ saw cut has 

 been made half wa\' up the cap as shown in Figure 

 2 and a piece of tin-plate, F"igure 5, inserted 

 in the slot. This piece of plate constitutes the 

 gnomon of the dial, and is pivoted at one end 

 by a nail passing through one corner as indicated. 

 The hole is drilled in such a position that, w hen the 

 gnomon is in use, the long straight side of the tin- 



FlGURE 4. 

 The development of the cylinder. 



these points are mere indentations in the wood, made 

 with some sharp instrument, they would quickly 

 become obliterated by dirt or usage unless some 

 distinctive marking were used. 



305 



