THE MICROSCOPE. 



139 



be placed over the mouth to exclude dust, and the bottle put in a 

 warm place for a day or two. My own plan is to put it — when 

 found just right — into collapsible tubes, from which the proper 

 amount can be squeezed out upon the slide, and in which it will re- 

 main of the same consistency until the last drop is used; but most 

 persons will prefer to dip it from a wide mouthed bottle with a small 

 glass rod, and to such I would strongly 

 recommend the capped bottle, which I 

 have named under the head of non-es- 

 sentials, as it excludes all dust, allows the 

 rod to remain in the balsam when not in 

 use, and prevents any foreign particles from 

 falling into the latter, as must be the case 

 in all bottles closed with a cork. 



And now we have brought our work 

 down almost to the final operation. Our 

 specimens are soaking in oil of cloves 

 waiting to be mounted, our glass is clean 

 and bright, our balsam in its bottle, our 

 forceps and needles lying in their places 

 ready for instant use. What more do we 

 need ? Only a lamp or other convenient 

 method close at hand for warming the 

 slide and cover; and some mode of centering the object 

 before applying the cover. The latter may be done by 

 laying a slide on a sheet of white paper or card board, and 

 drawing its outline with a pencil, and on removing the slide making 

 a mark exactly in the centre of this drawing. Of course, when the 

 slide is replaced, this mark will apparently be in its centre, and thus 

 the balsam and object can be accurately placed in proper position. 

 The principal objection to this method, is that the slide is apt to slip 

 out of place, and thus to render accurate centering almost impos- 

 sible. A most admirable contrivance for this purpose, however, is 

 the " porcelain mounting plate," n^med under the head of non-essen- 

 tials. This is made of a photographic porcelain plate, 3x5 inches, 

 ground flat upon one side, on which are cemented at right angles to 

 each other, two small strips of glass, the one three inches in length, 

 and the other one inch. A mark is then made upon the plate with 

 a pencil, exactly 1/2 inches from one strip, and Vn an inch from the 



Capped Bottle for Balsam. 



