72 H. J. Grayson : 



to its radial motion this carrier revolves axially, so that speci- 

 mens to be sliced may be tilted at any convenient angle in 

 relation to the slitting disc. This clamj^ also carries the 

 goniometric crystal holder (shown in the front right corner 

 of the tray) which permits of slicing or grinding in any de- 

 sired direction. The device for maintaining a steady pressure 

 or pull against the slicer coinprises the usual cord, weights and 

 pulleys, so placed as to be readily controlled. 



Lubrication of the slicer is provided for by means of a drip- 

 can and two pieces of sponge, one above and one below the 

 disc held in position by a spring clamp. 



Passing now to the grinding laps, of which there are two, 

 seen in the centre of the table, it will be noted that they are 

 screwed to the top of the spindles by means of a threaded boss 

 below" each plate. This mode of mounting allows the whole 

 surface of the lap to be utilised, and is a convenience which 

 has only to be once used to be appreciated. It not only allows 

 the utmost freedom of movement, but also aids in the main- 

 tenance of a true surface on the lap for a long time. The 

 spindles of the laps are somewhat shorter than that of the 

 slicer, their length being 12 inches, so that the lap surface is 

 about 3|^ inches above the table, which is a convenient height 

 for most operators. The mounting of the spindles is the 

 same throughout, and has already been described. Dust and 

 grit are excluded from the bearings by means of a special close- 

 fitting collar in each case. 



It will be seen that each grinding spindle is accompanied by 

 a pillar which supports a clamping device in which specimens 

 or blocks of glass are held so as to swing radially across the 

 laps. This permits of parallel grinding to a precise thickness 

 or definite form, and though not necessary for ordinary rock 

 slicing, it has. as already explained, a variety of uses where 

 precision is required. 



The lower portion of each rod is threaded, and screws into 

 a long socket let into the surface of the table. It can thus 

 be accurately raised and lowered during use, so as to maintain 

 a steady and even pressure upon the lap. It is also adapted to 

 carry the goniometer Avhich fits the special holder shown in 

 the centre tray, and. as already indicated, as every part of the 



