104 



G. H. Williams — Rock-cutting Machine. 



on a firmly constructed cross-piece from which they may be 

 readily removed for recharging. 



2. One one-eighth horse power electric motor of the Donald- 

 son-Macrae pattern (fig. 2). This is fastened to a second 



cross-piece above the bat- 

 teries and below the table 

 surface. It is provided 

 with two pulleys from 

 which belts pass to the 

 shafts on the table, which 

 carry the grinding disks 

 and diamond saw. 



3. The grinding appa- 

 ratus consists of two cir- 

 cular disks of solid copper, 

 9 inches in diameter and 

 f inch thick, which may 

 be used alternately as different grades of emery are required. 

 They are attached either by a screw or square socket to a ver- 

 tical iron spindle which revolves smoothly in a conical bearing. 

 The grinding disk is surrounded when in use by a large cylin- 

 drical pan of tin (not shown in the cut) which has an opening 

 in its center to allow of the passage of the spindle. 



4. The sawing apparatus consists of a horizontal counter- 

 shaft, placed on a different part of the table from the grinding 

 disk, and connected with the motor by a separate belt. It 

 carries at one end a vertical wheel of solid emery, and at the 

 other an attachment, level-table and guide for the diamond- 

 saw.* A small water-can and spout (not shown in the cut) is 

 suspended over the level-table to keep the edge of the saw wet 

 when it is in use. 



Under some circumstances it may be found advantageous to 

 obtain electricity for this motor by a direct wire from an elec- 

 tric light or power company. Considerable inquiry has shown, 

 however, that in Baltimore the storage batteries are more 

 convenient, safe and economical. A single charging lasts the 

 needs of a laboratory of ten students for a month. The 

 batteries are removed by the electric company and returned 

 with little or no delay at a cost of $3.75 for recharging. 



Petrographical Laboratory, 

 Johns Hopkins University, Dec. 10, 1892. 



* Admirable saws, circular tin disks 8 inches in diameter with one inch center 

 aperture whose edge is provided witn diamond crust secured by cement, may be 

 had of Wm. Kerr. No. 292 Westminster St., Providence, R. I., for $12.00 per half 

 dozen. 



