COPPER, STEEL, AND BANK-NOTE ENGRAVING. 609 



which is called a " cycloidal line," and may be described as that 

 line produced by a point revolving about a moving center. The 

 shape of the curved line depends upon the relative rate of speed 

 of the two motions, the circular one of the point and the forward 



Fig. 



-Open CycLoiOAi, J^ixk. 



Fi(i. ^. Wide Cycloikal Line. 



one of the plate. If the latter is comparatively slow, the cycloid 

 will take this shape (Fig. 8) ; if still slower, the curves will cross 

 each other instead of nearly touching. If the motion of the plate 

 is comparatively rapid, the cycloid will take the form of Fig. 9, or 

 one still more open. 



By repeating these lines and causing them to overlap each 

 other beautiful lacelike effects can be had, very difficult to imitate 

 by hand (Fig. 10). The patterns can be varied almost endlessly. 



Machine engraving of a far more intricate character is pro- 

 duced by the " geometrical lathe," which is one of the most deli- 

 cate and complex machines ever invented (Fig. 11). 



Americans have particularly distinguished themselves in me- 

 chanical engraving, and, in fact, it was one of our people a Mr. 

 Spencer, of Philadelphia who introduced the " bank-note en- 

 graving machine " in the early part of this century. This ma- 

 chine, however, was very primitive, as it had but one " cam," and 

 consequently was very limited in its possibilities as compared 



irs^^TT^r^nn 



Fig. 



-Cycloidal Line 



Fir. 10. Cycloidal Pattern. 



with those built in the present day, which have seven cams as 

 well as other attachments not dreamed of by Spencer. 



The geometrical lathe of the present day can not be described 

 so as to be perfectly understood, but something of an idea of its 

 working can be gained from the following : 



A tool, mechanically sharpened and shaped, made of hardened 

 steel, is used on this machine and is fixed solidly and immovably 

 in a rest, or carrier, over the chuck of the lathe. If the chuck 



