24 
MECHANICAL PORTION OF THE MICROSCOPE. 
centre of the cornea impair the distinctness of vision ; hence 
difficult test objects should always be viewed with the instru- 
ment inclined. An inclination of about 55° to the horizon 
generally affords the easiest position for protracted obser- 
vation. 
‘‘It is matter of surprise, (says Dr. Carpenter, in his treatise 
on the microscope,) that opticians on the continent of Europe 
have generally neglected this very necessary convenience in 
the arrangement of the microscope.” 
41. Stage. The stage should be large enough to support 
conveniently any object, and to bring any portion of the slide, 
on which the object is placed, into the field of view. The 
stages of many European microscopes are inconveniently 
small. Spring or sliding clips are required to retain the 
object in place when the instrument is inclined. If a mov- 
able stage is attached to the microscope, the movement should 
be smooth and steady in every direction, and the stage 
should remain steady as it is placed when the instrument is 
inclined. 
42. Adjustment ©f Focus. The mode of effecting the fo- 
cal adjustment should be such as to allow a free range of tw^o 
or three inches, to suit the focus of any object-glass, and there 
should be an arrangement for obtaining a delicate adjustment 
in every part of the range. To secure these objects a coarse 
adjustment, by rack and pinion movement, is generally em- 
ployed, and a delicate fine adjustment by a screw' acting upon 
the end of a lever. 
43. Simplicity and Facility of Adjustment should be 
secured in every part, and the instrument should be so arranged 
in its case that it can be taken out and fitted for observation 
with as little labor as possible. Many interesting objects are 
likely to pass unnoticed, if much time is required to unpack 
and adjust the instrument for observation. 
44. Description of Microscope Stands. Since w e have 
been engaged in the manufacture of microscopes, we have 
carefully examined the most approved forms of English and 
J. & W. GRUNOW & GO’S ILLUSTRATED 
