192 MICROSCOPIC ILLUSTRATIONS. 



(fig 1 . 16) to it. By means of the wheel and endless screw 

 let down the arm of the instrument till the body shall be 

 considerably below the aperture of the stage ; then take 

 off the lid of one of the aquatic boxes, and fix the other 

 part, first warmed at the fire, upon the stage; which 

 turn round on its pivot until its surface with the box 

 shall point downwards ; then insert a drop of the salt to 

 be viewed upon the inferior glass of the box (now, by 

 virtue of its position, the superior one) ; turn the boot 

 round on the lengthening piece until its projecting cone 

 shall look upwards, and adjust the focus by means of the 

 wheel and endless screw, which now performs this office, 

 while the rack- work used under other circumstances, for 

 the same purpose now only gives a traversing movement. 

 Many chemical actions, between various bodies, both 

 fluid and solid, may also be viewed in this way. More- 

 over, crystallizations, &c. can be seen under any of the 

 usual modes of mounting, by placing the salts or other 

 bodies, between the glasses of the aquatic boxes, with 

 the closed or pierced lids, as the occasion may demand 5 

 only, whenever there is evaporation or evolution of gas, 

 remember to employ the pierced lids. 



I think, nevertheless, that the best way of viewing salts 

 is to use the glass slip, with its frame (fig. 29), and 

 merely to rub the liquid salt over its surface, allowing it 

 to drip a little at an angle of 45, before it is placed in 

 the slider- holder. The glass must not be warmed in this 

 method; and the salt must be allowed to crystallize 

 very slowly, in its own natural way. By this process, 



