ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 429 



the cutter by means of a counterpoise. The stand, which carries tlie 

 holder, is fitted to a sHde having cross motion and fixing attachment so 

 that the specimen may be advanced towards the cutter, and also be 

 moved right and left. The " crystal holder " is the part to which the 

 specimen itself is attached. It consists of a round graduated metal 

 plate covered on the cementing side by a glass plate, and swivelled on a 

 horizontal axis. It may be fixed in any desired position, and the rota- 

 tion is read by means of a fixed index. The arm carrying the crystal- 

 holder can be rotated about a vertical axis, the adjustment being read 

 on a graduated half-circle. The compound holder is so designed that 

 both axes of rotation pass through the crystal so that its position in 

 space will be approximately maintained during the adjustment. To 

 render the soft iron disk capable of cutting rock it must be tempered 

 with diamond paste. This is done by slightly notching the periphery 

 of the disk with a knife and then rubbing on a paste made of diamond 

 splinters finely powdered in a mortar and mixed with oil. The machine 

 is then started at a low speed and the glass guard-plate of the crystal- 

 holder lightly pressed against the disk. This will cause a sufficient 

 number of diamond particles to enter into the soft iron so that the 

 machine is ready for use. When the disk has once been properly 

 dressed it will last for a long time and the width of the cut will not be 

 more than 0*4 mm. A cut from 4 to 5 sq. cm. will require about ten to 

 twelve minutes. If this speed is not reached the disk will have to be 

 dressed again. The best lubricant is petroleum. 



Winkel's Motor-driven Grinding^ Machine for Microscopical Sec- 

 tions.* — The shaft which carries the grinding- wheel and belt-pulley is 

 verticallv journalled on a cast-iron block fitted with three standino- and 

 fixing screws. The waste is received in a trough. The metal grinding- 

 •disks can be replaced by glass ones for fine grinding and polishing. 

 According to requirement the machine can be fixed above or below the 

 table. 



Automatic Grinding-attachment for Wulfing's Grinding Mach- 

 ine.! — This apparatus is made by the firm of R. Winkel, for operation 

 with the Wlilfing grinding machine whose principle is taken to be gene- 

 rally well known. 



AVhen specimens require to be ground for a long time or to be 

 ground extremely fine, it will be found rather inconvenient to guide the 

 grinding tripod over the plate. The attachment shown in fig. 65 has 

 therefore been designed for imparting to the tripod movements closely 

 resembling hand movements. A V-shaped bridge, which stands with 

 two vertically adjustable screws on the grinding-plate, carries two pins 

 extending upwards and engaging in corresponding eyes in the tripod. 

 The tripod stands free on the plate and may be weighted if necessary 

 by a couple of small weights. The bridge extends in a long metallic 

 bar which can glide in a sleeve movable in all directions. From above 



* Special Catalogue : Microscopes for Mineralogists ; Microtomes and Grind- 

 ing Apparatus Accessories. Carl Zeiss (Agents) London. 



t Special Catalogue : Microscopes for Mineralogists ; Microtomes and Grind- 

 ing Apparatus Accessories. Carl Zeiss (Agents) London. 



