52 



THE AMERICAN MONTHLY 



[March, 



filling the channels or tubules in the 

 wood. It' is obvious that the air must 

 be removed in some ^vay. This can 

 easily be eftfected by boiling the vs^ood 

 in w^ater. It will then be seen that 

 the water has filled up the pores of 

 the wood and made it transparent. 

 If the same piece of wood be placed 

 in glycerin and then examined, it will 

 appear still clearer. Another piece 

 may be placed in turpentine, and then 

 covered with balsam on a slide to 

 make a further comparison. 



If a piece of gi^ound glass be exam- 

 ined with a microscope, the surface 

 will appear very rough. A layer of 

 Canada balsam will cause the rough- 

 ness to disappear, because the parti- 

 cles that caused the rough aj^pearance 

 are now optically continuous, and the 

 light passes without interruption 

 through the glass into the balsam and 

 to the eye. In grinding sections of 

 hard substances, it is usual to polish 

 the surfaces intended for examina- 

 tion, but polishing is not always nec- 

 essary if the surface be covered with 

 balsam, for the scratches are then in- 

 visible. 



A few such observations as are 

 mentioned above will be invaluable 

 to the beginner in microscopical 

 mounting. They vsall teach him to 

 select the proper media for mounting 

 his specimens, which many persons 

 only learn after much waste of time 

 and inaterial. 



We shall describe the inethods of 

 mounting under four heads : i . Dry 

 mounting. 2. Mounting in gelatin- 

 ous media. 3. Mounting in resinous 

 media. 4. Mounting in fluids. 



As a rule, dry mounts are to be 

 used with light condensed upon them 

 from above the stage. When objects 

 are mounted to be examined by light 

 transmitted through them, as trans- 

 parent objects, they are seldom ex- 

 amined in any other way. Occasion- 

 ally, however, such specimens are 

 examined with light condensed upon 

 them from above, and some very 

 beautiful prepai-ations of this kind 

 can be made, as will be learned from 

 a future article. 



We have already several times 

 spoken of the beauty of specimens 

 rather than of their interest in a sci- 

 entific sense. It may be asked whe- 

 ther it be a principal aim of the mi- 

 croscopist to prepare beautiful objects. 

 Some persons may say there has been 

 too much of such work done by mi- 

 croscopists already ; the time could 

 be far more profitably spent in re- 

 search. We may regret that there 

 is not more thorough scientific work 

 in progress among the microscopists 

 of the country, but we would not, 

 therefore, despise the work of those 

 who, vs^ithout the intimate knowledge 

 of the biologist and the specialist in 

 science, find pleasui'e in the world of 

 rare beauty revealed by the micro- 

 scope. Theirs is a study of nature, 

 not deep, not fully appreciative, but 

 good, elevating, educating. There- 

 fore it is worthy of encouragement. 

 The preparation of a beautiful micro- 

 scopic specimen is worthy of emula- 

 tion, even though it be only that one 

 may have something beautiful to sho"w 

 to one's friends. Whatever is beau- 

 tiful exerts an influence tending to 

 elevate all who are able to appreciate 

 it. 



New Eye-piece Micrometer. 



Prof. W. A. Rogers, of Harvard 

 Observatory, has again laid micro- 

 scopists vinder obligation by making 

 an eye-piece micrometer for high 

 oculars. It is a cover-glass of proper 

 size to fit above the diaphi'agm of a 

 ^-inch or §-inch ocular, ruled in a 

 scale with the fifth and tenth lines 

 longer, and so fine as to need the 

 magnifj'ing power of the eye-lenses 

 to separate the lines well. The high- 

 povs^er ocular separates also the striie 

 of diatoins, or other minute subdi- 

 visions of objects, and the scale en- 

 ables one to count them with a 

 readiness and ease which has not 

 before been possible. It is a simple 

 and inexpensive thing that takes the 

 place of the most expensive spider- 

 web micrometers. 



J. D. C. 



