130 Transactions of the Boyal Microscopical Society. 
It would be no less a “ practical ” benefit if we were able in 
future to avoid some of the mistakes of recent years. Amongst 
these may be mentioned the views held up to the present day, that 
the resolution of lined objects depends upon the shadow cast in 
consequence of the obliquity of the light. Mr. Stephenson has 
reminded me of the derision (in which I joined) with which the 
object-glass of Mr. Tolies, with its marked aperture of 180^, was 
received ; and yet at that time the demonstration existed that the 
effective angular aperture of an object-glass may readily exceed 
180°. 
Another instance may be found in that vexed question of a few 
years since, the Aplanatic searcher. At the time it did not seem 
to me unreasonable in theory that the defects of an object-glass 
might within limits be neutralized in the way proposed. The 
practical reason for not accepting the invention was the absence of 
results in the hands of anyone but its inventor ; but no one was 
able to expound the principles, then well known elsewhere, which 
showed that its theory was unsound. If we had been aware of 
those principles we should have been able to discuss the claims of 
the invention in an intelligent manner and without having to 
depend solely on the want of results. 
What seems to me to make the subject the more tempting 
is, that it is virgin soil ; any of us who will take it up will not 
find it has been occupied before him, and the Society in receiving 
the results will not be in close competition as they are now with 
other Societies, — in fact, we should then be working in a field of 
our own, the want of which has been so often bewailed among us. 
The examination of diatom valves and Podura scales has un- 
doubtedly been the cause of many improvements in object-glasses, 
and the indiscriminate abuse sometimes showered upon the observers 
is to a great extent undeserved : at the same time it is certain that 
there has been much misdirection of time and energy in such 
examinations, so far as the end proposed has been only to see with 
one glass for the hundredth time as nearly as possible what has 
been seen a hundred times before by a hundred other observers. 
Such examinations, if properly directed, would have advanced the 
knowledge of microscopical phenomena in general many years. 
Of the two great methods of scientific inquiry, observation and 
experiment (or as they have been otherwise termed, “ passive and 
active observation ”), we have, I think, confined ourselves too much 
again (p. 207), dealing with the effect of a particular kind of illumination on 
mineral structures, he says that it “ would be equally applicable in the case 
of rods and minute fibres, and such kinds of structures as are commonly met with 
in organic boilies.” And (p. 209), “ Such general conclusions are more simple 
and obvious in the case of mineral structures, but are by no means confined to 
them .... and I cannot but think that much remains to be learned even in the 
case of more purely organic structures.” 
