J. B. JORDAN ON ROCK SECTIONS. 



187 



turning-lathe ; into the slot between them is placed a casting, B, 

 carrying the bracket for the angle-pulleys, C ; this casting is bored 

 to receive the spindle, D, which, by means of the treadle, is made 

 to revolve about 400 or 500 revolutions per minute. It is also 



bored to receive another spindle, E, to the top of which is fixed a 

 metal plate, F, for carrying the small cup, H, to which the speci- 

 men is attached by means of prepared was. I find that this means 

 of mechanically applying the work to the slicer is far preferable to 

 holding it in the hand in the ordinary way ; the requisite pressure 

 against the cutting disc is regulated by the weight G, and the 

 thickness of the slice by the thumb-screw, K, on which the spindle 

 rests. By this means, I am enabled to cut tolerably thin and 

 parallel slices — the thinness, of course, varying according to the 

 strength of the rock which is being operated upon. The slitting 

 disc is made of soft iron, eight inches diameter, and about ^L of an 

 inch in thickness, and it is fixed on the spindle D, between two 

 brass-plates four inches diameter, in the usual way. The operation 



