Dr, Goring on Microscopes. 205 
glasses I have described, I have two more of 1 and + of an inch 
focus, which Ihave not inserted, because (though executed with 
the utmost care,) they are no better than the common ones. I was 
grievously disappointed with these, for I had fully expected that 
the same principle applied to deep object-glasses would form as 
superior an object-glass for high powers as for low ones: however 
the reverse is the fact;—it is one of those things which can only 
be learnt from experience, and could not have been predicated @ 
priori. There is doubtless a reason for this, but I am not able to 
shew what itis. Still, therefore, the common object-glass is the 
best for high powers, viz., for those of a quarter of an inch focus, 
and upwards. My object-glasses are however deep enough for 
all ordinary objects—certainly for all opaque ones. There are, 
nevertheless, many transparent objects which cannot be seen with- 
out object-glasses of at least 1, inch focus,—such are many 
kinds of animalcules and the minute lines on the dust of a butter- 
fly’s wing, §c. For these the common single lens of small aper- 
ture will perhaps ever remain the only efficient object-glass,—an 
equivalent power obtained with my object-glasses, or those of the 
common construction of similar focus, by increasing the depth of 
the eye-glass will never shew the objects in question, because what 
may be called the penetrating power of a compound microscope 
depends upon the depth of its object-glass, as that of a telescope 
upon the aperture of the metal or glass which forms the image 
viewed by the eye-glass. The eye-glass either of a microscope or 
telescope merely developes what is contained in the image it 
enables us to view; it cannot of course render any thing sensible 
to our sight which does not exist in the spectrum formed by the 
object-glass or metal. I may here mention that I had previously 
constructed my microscope with one object-glass only of one inch 
focus, and got my powers by increasing the depth of the eye-glass 
as is done in telescopes. I however, found, that a large image 
viewed by a shallow eye-glass made a much better instrument 
than a comparatively small one (formed by a shallow object-glass), 
viewed by a deep eye-glass; indeed the same position holds good 
with regard to telescopes also, for the largest and longest (ceteris 
Vou. XVII. Q 
