188 MICROSCOPIC ILLUSTRATIONS. 



the instrument just described, is by far the best and 

 simplest with which I am acquainted for all sorts of 

 transparent objects, and should, therefore, always be 

 used when practicable ; and this observation applies to 

 all sorts of microscopes and engiseopes. Occasionally, 

 however, the weather is so dull and gloomy, that we see 

 better by artificial light : I therefore now give the 



2nd. Method of mounting for viewing transparent objects 

 by artificial light. — Setting out on the supposition that 

 the instrument has been just removed from its case, and 

 is in the position given in the plate, proceed as follows : — 

 Place it on a table ; detach the bar from the front leg, 

 as before ; move the mirror and condensing lens to one 

 side ; then turn the bar round till it assumes a hori- 

 zontal position, keeping the neck of the ball at the bottom 

 of the quadrant slit, in the position in which it is repre- 

 sented in the drawing : its rotatory action is the only one 

 at present required. This arrangement will leave the 

 space, both behind and before the stage, open for the in- 

 troduction of a lamp or candle, &c. The condensing 

 compound lens, f, attached to the body, together with the 

 plane-convex one, n, under the stage, and the mirror, 

 must remain inert and unemployed, in this as in the pre- 

 ceding mode of observation, and may be removed alto- 

 gether. Adjust the height of the instrument to suit that 

 of your light and eye, by drawing the tube of the pillar 

 in or out : place your light centrically behind the aper- 

 ture of the stage, at two, four, or six inches distant from 



