Sky Study 



915 



Another excellent observation lesson for teaching the fact that the sun 

 travels farther south in the winter, is to measure the shadow of a tree on the 

 school grounds at noonday once a month during the school year. The 

 length of the tree shadow can be measured from the base of the tree trunk, a 

 memorandum being made of it. 



14. When does the stick or tree cast its longest shadow at noon — in 

 December or February ? February or April ? April or June ? Why ? 



Topics for English themes — The size and distance of the sun. The heat of 

 the sun and its effect upon the earth. What we know about the sun spots. 

 Our path around the sun. 



Supplementary reading — Starland, Ball; The Earth and Sky, Holden. 



A sundial made by pupils. 



LESSON CCXXXIII 

 How TO Make a Sundial 



Method — The diagram for the dial is a 



lesson in mechanical drawing. Each pupil 



should construct a gnomon (no-mon) of 



cardboard, and should make a drawing of 



the face of the dial upon paper. Then the 



sundial may be constructed by the help of 



the more skillful in the class. It should be 



made and set up by the pupils. A sundial 



in the school grounds may be made a center 



of interest and an object of beauty as well. 

 Materials — For the gnomon a piece of 



board a half inch thick and six inches 



square is required. It should be given 



several coats of white paint so that it will 



not warp. For the dial, take a board 



about 14 inches square and an inch or more thick. The lower edge may 



be bevelled if desired. This should be given three coats of white paint, so 



that it will not warp and check. 



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, indicating the 

 hour. Take a piece of board six 

 inches square, and be very sure its 

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

 represent the four angles; drf.w on 

 it a quarter of a circle frorr 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 line 

 vw making the angle at x the same as 

 the degree of latitude where the sun- 

 dial is to be placed. At Ithaca the 

 The gnomon. latitude is 42°, 27' and the angle at x 



