204 THE MICROSCOPE. 



bar D moving backwards and forwards in the tube by 

 means of the screws c, c, serves, in conjunction with the 

 points F, F, to fix the specimen to be cut, which is effected 

 as follows : 



The cutting surface E, B, being slightly screwed up, as 

 shown in the drawing, and the bar D being drawn back 

 a sufficient distance, the specimen to be cut is placed in 

 the instrument, and firmly fixed by turning the screws 

 c, c ; it is then cut level with the surface by a proper 

 knife or chisel, and the table being screwed down one or 

 more divisions (as shown in the left-hand diagram), a 

 section is cut, and if found of sufficient thinness, a number 

 may be cut by continuing to turn the table down a similar 

 number of divisions, until it will screw no further, when 

 the table must be again screwed up, and the specimen 

 loosened and raised if more sections be required. The 

 principal points of the instrument are : 



1st. Its portability the tube being about two and a 

 half inches long by one inch in diameter. 2d. The 

 specimen to be cut is fixed once for all, and the cutting- 

 surface screwed down to it, a feature that will render it 

 peculiarly applicable to the cutting of soft substances. 

 3d. The ease with which a number of sections may be 

 cut without disturbing the specimen when once properly 

 fixed, while the size of the tube, and the facility with 

 which it can be adapted to objects of various diameters, 

 enable the operator to get sections of stems of plants, &c. 

 whole. In cutting sections of hard woods, which require 

 considerable purchase, the instrument may be placed in a 

 semicircular opening in the edge of the working-table, so 

 that the flat plate or cutting-surface may rest upon it, and 

 the strain thrown on the table. When used for cutting 

 soft substances, it can be held in the hand. 



Fig. 130 represents Mr. Gibbon's "Section-cutting Ma- 

 chine." It consists of a stout brass frame, A A, having 

 an opening in the top plate, for a tube B, half an inch in 

 diameter, and in depth one and a half inches. In this 

 tube a loose piston, c, works freely, and is steadied by the 

 slot seen in it. To a female screw D, motion is given by 

 the toothed wheel ; and the teeth of which, /?, answer 

 the triple purposes of thumb-milling, ratchet-stop, and 



