MACHINE FOR CUTTING AND GRINDING ROCK SECTIONS, 261 
making a sort of file. Water must be allowed to drop on the disc, 
but not too copiously. About a square inch of limestone may thus 
be cut in about twenty minutes, harder stone taking a proportion- 
Elevation. Fig. 54. 
Plan. Fig. 55. 
Plan of Grinding Disc. Fig. 56. 
Section of Grinding Disc. Fig. 57. 
ately longer time, but by exerting a greater speed I have done 
nearly twice as much in the same time. 
For grinding remove the cutting and substitute the grinding 
