ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 467 



part of the cover for the disk, to prevent the emery flying about. A 

 box beneath also catches the powder that falls. (This arrangement 

 is also supplied with fig. 88, though not shown in the woodcut.) 

 A second wheel at i, with a cord passing over Jc, actuates a vertical 

 spindle I, which rotates a horizontal cast-iron plate at m for polishing. 



Making- Sections of Rock, Bone, Ivory, &c.* — Mr. J. Smith 

 describes the following method of making and mounting transparent 

 rock-sections. The first step is, of course, to get a suitable piece of 

 rock, say a fragment of trap or basalt. This should be broken as thin 

 as possible, and to do this, having struck off a fragment from the 

 parent rock or boulder, take it between the fingers and thumb of the 

 left hand. Hold one edge on the rock from which it was struck, or 

 any hard stone which may be convenient, and strike it a sharp blow 

 with the hammer fair on the opposite edge. If this is well done thin 

 fragments about l-8th in. thick will fly off. 



The fragments of rock should be roughly clipped in the field by 

 wire nippers into disks of about 7-8ths in. diameter, and having reached 

 home the next thing is to make the disks roughly circular, and to 

 flatten and polish one side. To do this, a flat slab of polished sand- 

 stone, 18 in. square by 4 in. thick, is used, on which the edge of the 

 disk is rubbed, using water and giving it a slight turn at every rub ; 

 a very little practice will enable any one to make the disks almost 

 circular. But what is chiefly to be aimed at in making them circular 

 is to get a smooth edge, as a disk having a perfectly smooth edge will 

 noit break so readily in the subsequent process as a rough-edged one. 

 It should now measure about 5-8ths of an inch in diameter. The flat 

 face must nest be polished so as to remove every trace of scratching 

 caused by the sandstone, and it is necessary at the same time to make 

 this face perfectly flat. To accomplish this, a water-of-Ayr hone, 7 in. 

 square by 2^ in. thick, is used, having one of the faces perfectly flat. 

 On this face the disk is rubbed with water, until it also becomes 

 perfectly flat and free from scratches. It must then be made thoroughly 

 clean and mounted on a piece of hard wood (well seasoned beech 

 wood) 2 in. square by f in. thick. The disk is fixed to the block 

 with gum arable, putting plenty round the sides, so as to form a 

 collar, and allowed to harden for two or three days. 



The specimen is now to be ground down until the beech can be 

 seen distinctly through it. It will not do to rub it on the sandstone 

 now, as water would dissolve the gum, and the specimen would be at 

 once detached. For the purpose of rubbing it down use a flat metal 

 plate, coarse emery powder, and paraffin, turpentine, or benzoline, as 

 none of these substances will dissolve gum arable. After it has been 

 reduced to about l-20th in., more speed may be obtained by using a 

 Turkish whetstone sprinkled with a little of the finest emery powder, 

 rubbing on this till the wood may be dimly seen through the specimen. 

 At this stage, the specimen, wood, and whetstone are cleaned with a 

 piece of rag soaked in turpentine, and rubbed down on the bare stone, 

 using the same fluid, till the specimen is thin enough to be taken off 



* Journ. Post. Micr. Soc, ii. (1883) pp. 28-33 (2 figs.). 



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