Rock Section Cvttiiuj Airparatus. 69 



my paper describes, other than the iiddition of a prradiiated 

 circle and index point, it would be possible to undertake 

 exactly the same kind of work as that for which the Oxford 

 machine had been exclusively designed, and, as I think, with 

 greater facility and convenience; the parallel clamp, which 

 swings radially over the grinding disc of my machine, being 

 already provided with the requisite adjustments for securely 

 holding specimens requiring special serial treatment. Plate 

 XVII., Fig. 1, shows the relations and simplicity of this appar- 

 atus. The radial clamp, holding a glass plate, to which a 

 specimen is cemented, is seen in position over the grinding lap, 

 its relation to the latter being controlled and adjusted by means 

 of the graduated head on the top of the pillar to the right 

 of the lap. Fuller details of this appliance will be found in 

 Section 2 and in the explanation of the plates. Considerable 

 experience of gi'inding operations requiring not only pre- 

 cision but delicacy of touch and freedom of manipulation over 

 the surface of a rapidly revolving disc, convinces me that the 

 requisite conditions for precise work are not as fully provided 

 for as they might be ])y the slow and rigid traverse of Pro- 

 fessor Sollas' machine. Moreover, his grinding laps are very 

 small, being only lin. in diameter, and driven by hand. The 

 working of such a machine cannot but be inconvenient, seeing that 

 one of the operator's hands is fully occupied with driving the 

 machine, leaving only one hand free for controlling the various 

 adjustments of the machine screws, and for applying water 

 and the necessary abrasives, etc. These operations, if the 

 machine is to be efficiently worked, requires the unremitting 

 attention of more than one hand. The fact that Professor 

 Sollas is fully satisfied with the results he obtains does not, 

 I think, preclude the propriety of pointing out that eqvially 

 good results may be obtained from simpler and much less 

 costly adjustments, applied to an existing apparatus. 



I may say that in addition to the various processes just 

 described, my machine is admirably suited to all polishing 

 operations ; the comparatively high speed at which it is run 

 rendering it particularly effective for this class of work. 



The completed apparatus has now been in use for more than 

 two years, and as it has fully met expectations I venture to 



