OF MICROSCOPIC OBJECTS. 143 



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 tliem are exceedingly brittle and hard. He will 

 find the method before described equally applicable here, 

 and should take both horizontal and vertical sections. 



COAL. This substance is one of the most interesting 

 objects to the microscopist. It is, of course, of vegetable 

 origin ; and though it is in many cases in such minute 

 separate portions as to have lost all appearance of vegeta- 

 tion, yet it is very frequently met with in masses, bearing 

 the form, even to the minute markings, of wood, in various 

 directions. To see this and prepare it for microscopic re- 

 search, 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 daik 

 colour and opacity of coal render an extraordinary thinness 

 necessary, and so increase the liability to this accident. 



Mr. Slade recommends that the piece of coal, having been 

 smoothed on one side, be cemented on that side to a glass 

 slip by marine-glue of the best quality, quite free from 

 undissolved or foreign matter. Great care must be taken 

 to press out all air-bubbles, the coal breaking up at such 

 places as it gets thin, a hole resulting. It may then be 

 reduced in the usual way, and when thin enough mounted 

 in Canada balsam and covered by thin glass. 



Perhaps the best method which can be pursued is that 

 recommended in the Micrographic Dictionary, which is 

 as follows : " The coal is macerated for about a week in a 



