DESCRIPTION OF THE ACHROMATIC MICROSCOPE. Ill 



an upright manner, is filled with water. By this simple 

 contrivance, for which we stand indebted to Mr. Varley, 

 the plant is retained close against the interior surface of 

 the vessel, so as to admit of a magnifier of short focus 

 approaching it ; whilst in the space between the flat slip 

 of glass and the concave surface of the vessel, it will live 

 some months, without requiring any other attention than 

 merely adding a little water to replace that which shall 

 evaporate. 



In reflecting upon what has been stated, it will be 

 evident that there are two points in the constructing of 

 our microscopes well worthy of notice, as tending to 

 facilitate the whole of this operation, viz. that the stage 

 be removeable, and the stem, c, capable of being turned 

 round. 



When the phial-holder is mounted on a simple stand 

 for carrying only single magnifiers, it becomes a very 

 useful instrument for the above purposes ; as also for 

 the examination of the progress of crystallizations and 

 other chemical actions. In this mounting it is named 

 the Phial-Microscope; and as a mirror is not attached to 

 it, a lighted candle must be placed close to the end of 

 the tube, o, fig. 22. 



Sect. 5. On the polarizing Microscope, or Apparatus 

 made use of for viewing objects by polarized light under 

 the Microscope. — Few subjects in experimental science 

 have roused the attention of philosophers of the present 

 age more than that of the polarization of light. Its 



