for resolving Transcendental Equations. 431 



easily verified and secured by a spirit level and screw adjustments 

 at one or both ends. The straight edge IJ itself should be graduated 

 into equal parts, corresponding to decimals and centesimals of 

 the radius (1), to obtain which it is only requisite to measure the 

 length of 360° on the vertical scale as before obtained, and divide 

 the result by 2*- = 2 x314159, &c. It is likewise convenient that 

 the straight edge should have a screw motion in a horizontal direc- 

 tion, by which its error of zero may be destroyed without altering 

 its horizontal position. 



(10.) The fiducial line of the vertical scale, or that whose in- 

 tersection with the straight edge marks the values of A, ought to 

 be exactly vertical when the scale hangs freely. This condition 

 is not indeed essential to correct performance, provided it have 

 been graduated in its inclined position, but, if satisfied, it greatly 

 facilitates other essential adjustments, and may therefore be regarded 

 as one of those which must be gone through. It is very easy, all 

 that is needed being to make the lower end of the vertical scale 

 terminate in a narrow tail-piece of lead, which being flexible, we 

 may by bending it a little one way or other tilt the center of 

 gravity of the scale, so that the fiducial line shall coincide in 

 direction with a fine plumb line. 



(11.) The values of e may be read off" in two ways, either, first, 

 by a graduation on the slider itself, (in which the fixed part may 

 serve as a vernier to the moveable one,) or on the straight ed'^e. In 

 the former case the graduation must be, like that of the straight 

 edge, into decimals and centesimals of the unit radius determined 

 as above described, and the zero point must be ascertained as follows. 

 Set the straight edge IJ and the slider both horizontal by their re- 

 spective levels, adjust the index hand II to 0°, and bring the center 

 Ii of the excentric wheel as nearly as may be over C, the center 



