1892.] 



MICROSCOPICAL JOURNAL. 



28T 



the lacquer with a brush, as it leaves unsightly ridges. Nearly all 

 retort stands have light bases ; therefore remember that when the 

 " centre of gravity falls outside the base" you are very likely to 

 '' hear something drop." 



a. Frame of ground glass 

 h. Card reflector. 



EXPLANATION OF PLATE. 



c. Wire support for refl 



d. Clamp. 



By the way. a |-inch thin glass circle, if coated with the blue 

 lacquer and stuck on the lower end of the cylinder holding the 

 diaphragms (in a continental stand) with a little paraffin, makes 

 a orood '' moderator" for night work. 



MICROSCOPICAL MANIPULATION. 



Practical Points in Handling Objectives to Obtain 

 Best Definition. — If you want to compensate for thinner cover- 

 glass, set the systems of your objective further apart; or the same 

 purpose may be effected by lengthening the tube of your micro- 

 scope. If, on the contrary, you want to correct for a thicker 

 cover-glass, set the systems closer, or make your tube shorter. 



I. Thicker cover, longer tube, and opening systems tend to 

 over-correction. 



II. Closing systems, thinner cover, and shorter tube tend to 

 under-correction. 



For the recognition of under or over correction by the appear- 

 ance of the object, the writer has found the method of E. Gund- 

 lach to be of great practical value ; and he would urge careful 

 practical study of these appearances as affording a guide to the 

 kind of correction needed, whether " under" or " over." 



To illustrate the practical use of the above, suppose, for ex- 

 ample, a condition of under-correction of " general spherical ab- 



