MaiiKHeld.] 4-/0 [jan. 5, 



occur in the table. Values of /• are now computed for the difiFerent values 

 of the argument log. f,, but for the maximum zenith distance, and the 

 results laid off on the line B C, from tlu- point B; and against the points 

 thus found tlic arguments log [, are written. Along the line AB are written 

 the zenith distances. Equal increments of zeni'.h distance are represented 

 by unequal increments of the line AB, in order that the line AC, or line of 

 maximum corrections, may be a straight line. Call the co-ordinates of any 

 point of .1(7. d and r, and the distance AB, dm. Then 



d : dm = r : rm 



dm dm 



rm rm 



from which tlie distances of the arguments from the point A maybe deter- 

 mined. The line AD represents the edge of a ruler, or a thread, stretched 

 from a needle at the point A. If this line be turned about A, until it passes 

 through that point BC, corresponding to the value of log o for which the 

 correction is sought, the correction will be the length of the perpendicular 

 to AB, measured to its intersection with AD, at the point corresponding to 

 the given zenith distance. 



This method has the advantage tl'at the interpolations are made separ- 

 ately, and will undoubtedly give good results, if '.he diagram is drawn 

 carefully, and large enough. 



or(f=-r= _-- R^(,,m-^,J (6) 



