1838.] Bates Medal-ruling Machine. 657 



misplaced one-tenth of an inch out of the centre of the picture. As an 

 example I have engraved two ruled images of a medal of Homer, be- 

 longing to Mr. Lang, C. S. with the deviation or distortion thrown in 

 opposite directions. Few will believe that they represent the same 

 object ! In running down the relief (as in the cavity of the ear, and 

 the front of the forehead,) it will be seen that the engraved lines return 

 and cover a part of the plate already engraved ! There is to be sure 

 an attempt to diminish the fault by lessening the deviation of the en- 

 graved lines : — thus, the one-tenth altitude may be made to give a devia- 

 tion of only one-twentieth or one-thirtieth in the engraving (by lessening 

 the angle of axis B — but the light and shade will be thus equally dimi- 

 nished, and the whole effect destroyed. 



The mode in which Mr. Bate junior got rid of this difficulty in his 

 patent instrument is then described — and it was its ingenuity which 

 alone led me to send for one of the instruments to rule my Bactrian 

 coins, rather than attempt to make one for myself, which I shall now 

 be compelled to do. 



" My son, observing, that the thing to be desired was, a means of bringing 

 the tracer down upon the medal, a quantity 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, — pro- 

 posed taking inclined sections of the medal. A little consideration determined 

 the selection of 45°, as being equidistant from the vertical and horizontal posi- 

 tions employed and this inclination completely fulfilled the purposes required t 

 removing the distortion altogether, and so far from impoverishing the effect of 

 light and shade, improving that effect, inasmuch as without diminishing its 

 quantity it threw the light upon the representation of the medal at an angle of 

 45° to its plane, instead of as before in the direction of the plane of the medal*. 

 The arrangement finally adopted is represented in fig. 2. 



" The tracer c being now attached to the right-angled triangle efg and a 

 friction roller substituted for it at h, the triangle (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." 



Nothing could be more simple, efficient and correct than this im- 

 provement, and though the merit of it has been contested by the French 

 and by the Americans, I thought Mr. Bate justly entitled to his patent 

 (of which by the way I have seen no specification yet in the Repertory) 

 and willingly acceded to the terms he enjoined to my friends in Eng- 

 land on consenting to make me one, — namely, that I should not make 



B i3 a second axis fixed on A at any convenient angle, carrying the arm which 

 holds the diamond point or graver. 



* This is not so comprehensible —the effect of light and shade depends 

 merely upon the amount and direction of the deviation : and the smaller the 

 relief of a medal, the more horizontally the light is required to fall on it in order 

 to exhibit parallel effects to those of more angular light on a high relief. 



