Condition of Microscopy in England. By Frank Cris]). 129 
So simple a matter as the experiences of Welcker on the effects 
produced by globules of air or oil immersed in a fluid of greater 
or less refractive power than themselves, has enabled subsequent 
observers to distinguish more readily and with more accuracy 
elevations from depressions, and to determine the true structure of 
a large class of objects, so that vacuoles need no longer be mistaken 
for nuclei. 
The supposed tubular structure of human hair can be shown to 
be erroneous by the application of such principles, and the belief 
in the solidity of the lacunae of bone was disposed of by a con- 
sideration of the refractive effects of Canada balsam. 
The determination of the refractive index of a substance will 
often show that it belongs to one class of bodies, such as the 
albuminoid, and not to another, and enables proper deductions to 
be drawn of the real as opposed to the apparent size of cavities, 
such as those in the interior of starch grains. If an object exhibits 
double refraction it cannot be fluid, and the examination of mus- 
cular fibre by polarized light will determine whether it is at rest or 
in the state of contraction. 
A paper by Mr. Lowne, just read before the Eoyal Society, 
on the “Eyes of Insects,” will furnish another instance of the 
assistance the naturalist would derive from being able to refer to 
an established theory of microscopical observation, an important 
part of the conclusions come to in the paper turning upon the 
results of experiments on the effects manifested by the transmission 
of light longitudinally through glass tubes and threads.* 
Our friends the histologists have arrived, as some of them con- 
ceive, at the limit of the resolution of structure ; and my senior 
colleague, who is ready to seize with such avidity on any process 
that seems to indicate the possibility of further knowie^e on 
histological subjects, would, I am sure, rejoice if he could be 
guaranteed the power of determining more of the ultimate structure, 
say of a muscular fibre, than he is now able to do. 
I believe that guarantee might be given if the work I am 
advocating were undertaken, and that it would be found in the 
result that the histologist best grounded in such work was the best 
authority in the determination of Structure,! and many at present 
obscure problems would be in a fair way of solution. 
* Since printed in ‘Proc. Roy. Soc.,’ vol. xxvii. 261. 
t Since this paper was written I have seen the lecture on “ Microscopes ” (in 
vol. i. of the ‘ Science Lectures at South Kensington’), by Mr. Sorby, F.R.S., the 
late President of this Society, in which he points out (p. 203) that “ much may 
be learnt by the study of mineral structures, since in the case of crystals and of 
solid portions of glass and other analogous objects we know what their character 
is, whereas in the case of minute organic structures we have rather to infer wliat 
is tlieir structure from what we see; therefore, in forming some general idea of 
illumination, I think we may learn a great deal by studying what we see in 
small crystals and in inorganic bodies of pretty well known form.” And 
VOL. I. L 
