PROJECTS 



567 



be moved ever so little up or down, either the nail or the knife- 

 blade will cut off the light of the star. 



Now you are ready to draw three lines on the face of the board, 

 and you probably will need an artificial light. With a ruler, draw 

 a line exactly corresponding to the plumb line (KL). Then draw 



FIGURE 1 



a straight line from the point of the nail to the edge of the knife 

 blade (KT). With a carpenter's square, draw a line (TU) at right 

 angles to the plumb line. The number of degrees in the angle at T 

 will be approximately equal to your latitude. If you haven't a 

 protractor to measure this angle, take the board to the laboratory 

 and measure the angle. 



EXPLANATION. If we could draw a line from the center of the 

 earth to the point where we stand (KL, Figure 2), we should have a 

 line running "straight down" (p. 24). Since the weight of a plumb 

 line points to the center of the earth, the direction of the plumb line 



