NATURE-STUDY REVIEW 



[17:1— Jan.. 1921 



HOW TO MAKE THE GNOMON 



The word gnomon is from a Greek word meaning "one who 

 knows." It is the hand of the sundial, which throws its shadow 



on the face of the dial, indi- 

 cating the hour. Take a piece 

 of card-board six inches square 

 and be very sure its angles 

 are right angles. Let s, t, u, v 

 represent the four angles 

 draw on it a quarter of a 

 circle from s to u with a radius 

 equal to the line vs. Then 

 with a cardboard protractor, 

 costing fifteen cents', or by 

 working it out without any 

 help except knowing that a 

 right angle is 90", draw the 

 The gnomon j-^^ ^^ making the angle at x 



the same as the degree of latitude where the sundial is to be placed. 

 At Itliaca the latitude is 42°, 27' and the angle at x measures 

 42° 27'. Then the board should be cut off at the line vw, and later 

 the edge sw may be cut in some ornamental pattern. 



TO SET UP THE SUN-DIAL 



Fasten the base of the gnomon by screws or brads to the dial 

 with the points of the gnomon at F, G, and the point v of the 

 gnomon at M, M', so that the point W is up in the air. Set the 

 dial on some perfectly level standard with the line A, A" extending 

 exactly north and south. If no compass is available, wait until 

 noon and set the dial so that the shadow from W will fall exactly 

 between the points A, B, and this will mean that the dial is set 

 exactly right. Then with a good watch note the points on the arc 

 E, K', on which the shadow falls at one, two, three, four, and five 

 o'clock: and in the morning the points on the arc J' D on which 

 the shadow falls at seven, eight, nine, ten and eleven o'clock 

 Draw lines from M to these points, and lines from M' to the points 

 on the arc E K'. Then place the figures on the dial as indicated 

 in the spaces between the two inner circles. The space between 

 the two outer circles may be marked with lines indicating the half 

 and quarter hours. The figures should be outlined in pencil and 

 then painted with black paint, or carved in the wood and then 

 painted. 



