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be removable like the rack and be replaced when worn. I am aware 
that there are certain difficulties of fitting, but with care and good 
workmanship these may be overcome. It will be said that the collar 
through which the shaft passes may be, and usually is, sprung ; that 
is doubtless an advantage, but my experience is that it is not entirely 
a remedy. Again, it will be said that every Microscope has tighten- 
ing screws to meet this very difficulty ; so it has, and very admirably 
they act the first time they are used ; but afterwards something wears 
away ; if the screw be of harder metal than the shaft, or whatever it 
presses on, it gradually cuts a little channel, and that channel is cut 
in the place where it touches when the Microscope is at the elevation 
at which it is most frequently used ; so that the instrument will hold 
its focus beautifully in every position except the one in which its 
owner requires to use it. I suggest that these screws should be of 
much softer metal than what they press upon, so that they may 
wear away instead of wearing it, and that a few duplicate screws should 
be supplied with each Microscope, which could be substituted when the 
original ones are worn out ; and they might well have some mark on 
the outside to show when they have been inserted to the extent of 
their capacity, and are no longer useful. The moral of all this is that 
the coarse-adjustment is as important as it ever was ; and that hard 
metal and good workmanship are not less valuable to-day than they 
were years ago, and are worth paying something to obtain. There is, 
however, another aspect to this matter; and I venture to ask a 
question which I fear many of my hearers will consider rather a wild 
one ; namely, Is it absolutely necessary that the whole weight of the 
movable part of the instrument should be borne by the coarse-adjust- 
ment ancl the tightening screws ? Is it beyond the power of human 
ingenuity to find some satisfactory method of supporting that weight 
without having recourse to pressure on the faces of the shaft ? Can- 
not we hope for the time when all the coarse-adjustment will have to 
do will be gently and evenly to move parts the weight of which is 
supported or balanced by other means ? I do not see that it is 
impossible, and it seems to me to be well worthy of the careful 
consideration of constructors ; the Wale stand was an ingenious step 
in this direction, but failed for want of rigidity, &c. If we could 
attain this end we might then indeed have an absolutely efficient 
coarse-adjustment which practically would not wear out. 
The next point which I wish to mention is the working distance 
afforded by the objective. I fear that in the struggle for definition 
this is a good deal lost sight of ; it is quite true that with high-power 
objectives, by which, for this purpose, I mean everything above a 
quarter of an inch, if one has distance enough for the object and the 
medium, if any, which it is immersed in, and the cover-glass, that is 
all that is requisite ; unless indeed we could obtain sufficient distance 
to use reflected light with high powers, of which there does not appear 
any immediate prospect ; but the requirements of modern ana- 
