290 On Mr. Bate's Improvement in Medal Ruling. 



a means of bringing the tracer down upon the medal, a quan- 

 tity equal to the deviation of the etching-point from the straight 

 line upon the plate; observing also that the process he was 

 employing transferred vertical sections of the medal to the 

 plate, — proposed taking inclined secti©ns of the medal : a little 

 consideration determined the selection of 4-5°, as being equidi- 

 stant from the vertical and horizontal positions employed, and 

 this inclination completely fulfilled the purposes required, re- 

 moving the distortion altogether and, so far from impoverish- 

 ing the effect of light and shade, improving that effect, inas- 

 much as, without diminishing its quantity, it threw the light 

 upon the representation of the medal at the angle of 45° to its 

 plane, instead of, as before, in the direction of the plane of the 

 medal. 



It was, however, soon found necessary to restore the tracing- 

 point itself to the vertical position with respect to the plane of 

 the medal, to allow of its being brought into every part of the 

 surface which it had to rule, and, for the same reason, the me- 

 chanism which gave motion to it was obliged to be removed 

 and the hand to be employed in its stead ; the arrangement 

 then became similar to the following diagram : 



u 



A- 



m 



10 



The tracer c being now attached to the right-angled trian- 

 gle e 9 f,g and a friction-roller substituted for it at h, the tri- 

 angle (the motion of which was strictly confined to the plane 

 of the diagonal e,g) moved d a quantity always equal to the 

 distance of the tracer c from the perpendicular p; so that the 

 etching-point described precisely the same line upon the plate 

 b as the tracer described upon the surface of the medal a, in 

 the following manner : — so long as the tracer moved upon the 

 plane surface of the medal, equidistant and parallel lines were 

 described upon the plate, as before; but the moment the tracer 

 rose above the plane surface of the medal, it began to deviate 



