TRANSPARENT ROCK-SECTIONS. 31 



at which one is most apt to lose his temper, for if the stone 

 is a hard one, progress is very slow; the rubbing must be done very 

 gently. If the digestion is at all out of sorts, the destruction of 

 the specimen is all but certain, and if a single grain of emery 

 lingers about the whetstone, the thin and transparent section will 

 inevitably be cut in two. Lately, I have fallen on a plan which 

 has proved an almost perfect cure for impatience and ill nature, at 

 this critical stage of the proceedings. It is this : — Keep a dozen 

 specimens advancing one after the other. When you have become 

 tired of one, lay it down and take up another. Strange as this 

 may appear, it is quite a cure for impatience ; and besides, more 

 progress may be made with a dozen, than by working with one 

 specimen only at a time. 



I may say here that in making sections of flints, agates, and 

 stones of like hardness, it is of no use rubbing them on the 

 sandstone ; they must be ground down from the very first on the 

 iron plates with emsry. The rest of the process is the same as 

 has been described above. 



I fancy that diamond-dust would be the disintegrator par 

 excellence, but have never indulged in this luxury. 



When the specimen is thin enough, and the beech can be well 

 seen through it, I give it a few light rubs on the Water-of-Ayr 

 stone, using water. The specimen can then be taken off the wood 

 and mounted in Canada Balsam, under a thin cover glass. 



Remove with a wet cloth all the gum from the edge of 

 the specimen, and thoroughly clean the wood of all impurity. 

 Boil the kettle. Stick the blade of a pen-knife into the side of 

 the beech, to act as a handle, and hold the specimen in the steam 

 from the kettle-spout till it condescends to slide down the face of 

 the wood. There need be no fear of its faUing off. The 

 water from the steam will prevent this. It may come off in 

 less than five minutes, or it may take half-an-hour. Do not get 

 impatient. To beguile the time, you may theorise about the size 

 and number of the imaginary spaces that intervene between the mole- 

 cules, or atoms, that build up the rock, and the size of the water 

 molecules which are trying to find their way through these spaces, 

 in order to dissolve the gum arable fixing the specimen to the wood. 

 If the specimen takes a long time to come off, you are very apt to 



