706 SUMMARY OF CURRENT RESEARCHES RELATING TO 



main shafting, shown in Plate XXII., is speeded down to about 300, a 

 convenient speed for the driving-wheels of both lathe and rock-slicer. 

 The usual method of gearing to a secondary shaft by means of belts 

 and loose pulleys has been dispensed with, and a system of connecting 

 directly to the main shaft adopted. This permits of any single portion 

 of the section apparatus being run separately ; the remaining cords and 

 pulleys being stationary. This effects a saving of power, and reduces 

 the wear and tear upon the machine and belts or cords. The sheer, and 

 each grinder and the polisher, are hence directly connected to the 

 principal shafting, which runs loosely through each driving-pulley, when 

 the latter are not engaged. These pulleys are thrown into action, each 

 by its own clutch, which is operated by a loose coned sliding collar on 

 the main shaft. The sliding cone is moved directly from the work- 

 table by means of a rod, to the lower end of which a lever handle-bar is 

 rigidly screwed in a convenient position. At the top of the rod is a 

 forked lever with adjusting screws fitting a groove in the sliding cone. 

 By a twist of the handle-bar below, the cone is forced under the lever of 

 the clutch, which tightly engages the hub of the driving-wheel, and the 

 lap or sheer, as the case may be, is brought into immediate action ; the 

 reverse movement, of course, instantly disengages the clutch, and the lap 

 or sheer becomes stationary. The photograph (Plate XXII. ), which 

 shows a portion of the main shaft, driving-wheels, and clutches, will 

 serve to make this portion of the mechanism sufficiently clear. 



Connexion between the driving-wheel and each spindle, by means of 

 a leather cord, is easily effected, the latter passing directly from wheel to 

 spindle with the aid of guide pulleys only, these being secured to the 

 under-surface of the table. 



Provision was originally made for two speeds, the change being effected 

 by means of split pulleys on the spindle, which can easily be removed 

 if required — but this is seldom necessary. A uniform speed of about 

 980 revolutions per minute has been found in every way satisfactory. 



An extremely useful adjunct to the rock-slicer is to be found in the 

 small emery grinder attached to the same bench (seen to the left of 

 Plate XXL), and driven in the same manner. It is speeded up to 2000 

 (or more) revolutions per minute, and has been found most convenient 

 for a variety of work for which the larger machine is not so well adapted. 

 It may be provided with various grinding and cutting wheels, as well as 

 polishers and brushes, which fit it for use upon fossils, and the grinding 

 and polishing of small mineral and other specimens. This is an addition 

 to its varied usefulness in the workroom generally." 



Method of Slicing, Grinding and Mounting Rock-sections.* — The 

 following is a summary of the salient points adopted by H. J. Grayson 

 when working at rock-sections : — 



" A. Charging the Slicers, etc. — This is invariably done with diamond 

 powder, which it pays to crush, and sift from time to time during the 

 operation. The sifting is easily done with the aid of several bits of glass 

 tube about 1 in. long and £ in. wide, to one end of which, after grinding 

 level, a bit of very fine bolting silk has been cemented. A sheer charged 

 with properly graded diamond powder cuts faster and cuts longer than 



* Proc. Roy. Soc. Victoria, xxiii. (1910) pp. 65-81 (4 pis.). 



