OF MICROSCOPIC OBJECTS. 



branching out, with straight points somewhat resembling the hairs 

 from certain caterpillars. But, of course, when the metallic-look- 

 ing gorgeous colours are all that is required to be shown, and re- 

 flected light used (as with the feathers of the humming-bird, 

 peacock, &c.), it is much better that they should be mounted dry, 

 as in Chapter II. 



The seeds and pollen of plants are most frequently mounted dry 

 as mentioned in Chapter II. ; but the more transparent of the for- 

 mer, and the darker kinds of the latter, are perhaps better seen 

 in Canada balsam. There is nothing particular to be observed in 

 the manipulation, except that the glass cover must be applied 

 lightly, otherwise the grains may be crushed. There are some 

 objects which cannot be shown in a perfect manner when mount- 

 ed dry, but when immersed in balsam become so very transpa- 

 rent that they are almost useless. To avoid this, it has been re- 

 commended to stain the objects any colour that may be conve- 

 nient, and afterwards mount in balsam in the ordinary man- 

 ner. 



Most objects intended for the polariscope may be mounted in 

 Canada balsam ; but there are some exceptions to this. Many of 

 the salts are soluble in this medium, or their forms so injured by 

 it, that glycerine or oil has to be used (see Chapter IV.) ; others 

 must be left in the dry form, as before mentioned ; and some few 

 it is impossible to preserve unchanged for any length of time. 

 Crystals, however, are amongst the most beautiful and interesting 

 subjects for polarisation ; and it is very probable that, by the aid 

 of the polariscope, new and valuable facts are yet to be made 

 known. For one who finds pleasure in form and colour, there is 

 a field here which will only open wider upon him as he advances ; 

 and instead of being in anywise a merely mechanical occupation, 

 it requires deep and careful study. The little here said on the 

 subject will show this in some degree. 



With almost every salt the method of crystallization must be 

 modified to obtain the best forms ; I may even go further than 

 this, and say that it is possible to change these forms to such a 

 degree that the eye can perceive no relationship to exist betwixt 

 them. If a solution of sulphate of iron is made, a small quantity 

 spread evenly upon a slide, and then suffered to dry whilst in a 



