Objects for the Microscope. 229 



rhombic prismatic system, but are various in form and size. 

 They polarize light splendidly. 



NITRATE OF POTASH, NITRE, OR SALTPETRE. 



This salt is dimorphous ; it crystallizes in various forms, 

 but they all belong to the right rhombic prismatic system ; 

 sometimes six-sided prisms with dihedral summits are on 

 the slide, and sometimes obtuse rhombohedral crystals, 

 resembling those of nitrate of soda ; but they all polarize, 

 and exhibit the phenomena of analytic crystals. 



Analytic crystals are those which possess the power of 

 analyzing light, like the tourmaline used in the ordinary 

 polariscope. 



SALICINE, 



an alkaloid extracted from the bark of the willow tree, and 

 crystallizing in beautiful forms, either in discs exhibiting the 

 cross and concentric circles of colour, or in prismatic crys- 

 tals in stellate and irregular groups, polarizing admirably. 



NITRATE OF SILVER, 



crystallized on a slide, shoots over the glass in most bril- 

 liant feathery crystals, and is also a splendid object viewed 

 with a spotted lens or parabolic reflector. 



I RECOMMEND THE FOLLOWING OBJECTS AS THE CONTENTS 



OF A GOOD EDUCATIONAL Box : 



Cuticles of Lily, Candytuft, and one or two others, to 

 show cells and stomata. 



Cuticle of Indian Corn, or Equisetum, to show siliceous 

 cuticle. 



Cuticle of Hyacinth, to show raphides. 



Cells of spiral fibre. 



Scalariform vessels. 



Starch grains. 



Hairs of Deutzia leaf. 



Scales on leaf of Elaagnus or Tillandsia. 



