200 MICROSCOPIC ILLUSTRATIONS. 



The direct light of the sun is utterly improper for 

 exhibiting - opaque bodies, being polarized and decom- 

 posed by them, so as to give rise to all sorts of optical 

 deceptions : neither can it be modified or dulled by 

 refraction through rubbed glass, or any sort of semi- 

 pellucid substances, and thus rendered fit for use : by 

 reflection from white toipolished surfaces it may, but it is 

 then no stronger than the light of the atmosphere. 



6th. Method of observing Opaque Objects by Day-light, 

 plain or condensed. — Employ the mounting (No. 2) recom- 

 mended for transparent objects by artificial light. 



If your object is contained in a slider, insert it into the 

 holder in the usual manner : turn your back diagonally 

 towards the window, and place the engiscope on a table, 

 in a convenient position for observation in that direction, 

 so that the light of the window may fall full upon your 

 object, without being intercepted by your head : the 

 nearer you are to the window the better, provided its 

 direct light does not get into your eyes. You then pro- 

 ceed to the adjustment of the focus, &c. as before de- 

 scribed. If your power is considerable, or the day dull, 

 you will require a condensed light : to obtain it, attach 

 the condenser, '/*, to the neck of the body, by means of 

 its clamping screw and split socket, 'g ; unscrew the 

 double convex lens from the other, and remember to use 

 only the piano- convex, with its plane side presented 

 towards the light, and its convex side towards the object : 

 slide it up or down upon the neck of the body; and adjust, 



