OF MICROSCOPIC OBJECTS. 95 



got with the watch-spring saw first, when the smooth " sharpening 

 stone " may be used to polish one side, which is easily accomplished 

 with water only. When this is effected, it must be washed clean, 

 and thoroughly dried, and then may be united to the slide in the 

 same manner as before recommended for the Orbitolite, &c. If 

 it is ever necessary to displace it on account of inequalities, bub- 

 bles, or other remediable fault, this may be done by warming the 

 slide ; though too much heat must be avoided, otherwise fresh 

 bubbles will certainly be produced. The covering with thin glass, 

 balsam, &c., will present no difficulty to the student ; but he must 

 remember that the transparency is somewhat increased by this 

 last operation. 



Corals are often treated in this way, in order to reveal their 

 structure. Except, however, the student has had much practice, 

 he will often find this a most difficult task, as many of them are 

 exceedingly brittle. He will find the method before described 

 equally applicable here, and should take both horizontal and verti- 

 cal sections. 



COAL. This substance is one of the most interesting objects to 

 the microscopist. It is, of course, of a vegetable origin ; and 

 though this is in many cases of such minute separate portions as 

 to have lost all appearance of vegetation, yet it is very frequently 

 met with in masses, bearing the form, even to the minute mark- 

 ings, of wood, in various directions. To see this and prepare it 

 for microscopic research, a suitable piece of coal must be obtained ; 

 but in every case the cutting and preparation of these sections 

 require great care and skill. Sometimes the coal is first made 

 smooth on one side, fastened to the glass, reduced to the requisite 

 degree of thinness, and finished in the method before described. 

 This mode of treating it is sometimes, however, very tantalizing, 

 as, at the last moment, when the section is about thin enough, it 

 often breaks up, and so renders the trouble bestowed upon it 

 fruitless. The dark colour and opacity of coal render an extra- 

 ordinary thinness necessary, and so increase the liability to this 

 accident. 



Perhaps the best method which can be pursued is that recom- 

 mended in the " Micrographic Dictionary," which is as follows : 

 " The coal is macerated for about a week in a solution of carbonate 



