OF DIALING. 



449 



to B e, making an angle of 23J degrees with the 

 side B d of the arm when the sun's declination 

 is 235 degrees ; it is plain, that if the length of the 

 arm be B d, the least breadth that it can have, to 

 keep the edge B e of the shadow B e g d from going 

 off the side of the arm d e before it comes to the end 

 e d thereof, must be equal to e d or d B. But, in order 

 to keep the shadow within the quarter divisions of the 

 hours, when it comes near the end of the arm, the 

 breadth thereof should be still greater, so as to be 

 almost doubled, on account of the distance between the 

 tips of the arms. 



To place the hours right on the arms, take the fol- 

 lowing method : 



Lay down the cross a c b d on a sheet of paper ; and 

 with a black-lead pencil, held 

 close to it, draw its shape and 

 size on the paper. Then taking 

 the length a e in your com- 

 passes, and setting one foot in 

 the corner A, with the other 

 foot describe the quadrantal 

 arc e f. Divide this arc into 

 six equal parts, and through 

 the division marks draw right 



4 



lines a g, a h, &c. continuing 

 three of them to the arm c e, which are all that can fall 

 upon it; and they will r eet the arm in these points 

 hrough which the lines t'.at divide the hours from each 

 other (as in former figure) are to be drawn right across 

 it. 



Divide each arm, for the three hours it contains, in 

 the same manner; and set the hours to their proper 

 places (on the sides of the arms,) as they are marked 

 in the previous figure. Each of the hour spaces should 

 be divided into four equal parts, for the half hours and 

 29. 



