ZOOLOGY AND BOTANY, MI0RO8COPY, ETC. 
391 
substitution of another objective in a much shorter mount increased the 
tube-length from 4^ to in., which, if not allowed for, would introduce 
errors amounting to 60 per cent, in the calculated powers. 
Perhaps this may be considered an extreme case, but it serves to 
emphasize the importance to the microscopist of knowing something 
more about the optical length of his instrument tube than can be 
ascertained by comparing its outside dimensions with a foot rule.” 
(6) Miscellaneous. 
Microscopy at the World’s Fair.* — Mr H. L. Tolman chose this 
subject for an address to the Microscopical Section of the Chicago 
Academy of Sciences. He said : — 
“ About eighteen months ago the Illinois State Microscopical Society 
decided to make a representation at the coming Columbian Exposition, 
and appointed a committee of three, consisting of Dr. L. D. McIntosh, 
Mr. C. 0. Boring, and myself, to solicit exhibits. On the death of 
Dr. McIntosh Mr. W. H. Summers was appointed in his place. The 
design of the Society was to take the requisite space at the World’s 
Fair and then ask all the Microscope makers in Europe and the United 
States to make a display of their productions, and also, if possible, to 
get exhibits of mounted slides, &c., from various workers in different 
departments of science. I spent last summer in Europe, and as chairman 
of this committee, and also as member of a similar committee appointed 
by the American Microscopical Society, I visited all the leading European 
Microscope makers, with one or two exceptions, and was very much 
pleased to see the interest they took in the matter. Several said they 
would rather make an exhibit in such a scientific display than in the 
commercial department, and it is probable that nearly all will be repre- 
sented. In fact, it is safe to say that the exhibit of modern instruments 
and accessories will be the most extensive that has ever been made at 
any world’s fair. 
In regard to a display of old instruments, unfortunately nothing 
could be accomplished. There are only three large private collections 
of Microscopes in Europe. By far the largest and finest, not only in 
England, but in the world, is that of Mr. Frank Crisp, a prominent and 
wealthy London solicitor. It contains over 2000 Microscopes, besides a 
very large number of substage attachments, condensers, micro-spectro- 
scopes, live-cages, mechanical stages, polariscopes, objectives and other 
accessories, which give an accurate history of the Microscope and its 
development. An evening spent with Mr. Crisp and his collection is 
one long to be remembered. Many of these instruments are very fragile 
and complex, not a few are unique, and it would be impossible, without 
great time and expense, to box and ship them anywhere. Some, on 
account of their fragility and complexity, could not be transported at all, 
and hence Mr. Crisp said he felt compelled to decline even to attempt 
to send his collection to Chicago. 
The next largest collection is that of Mr. Nachet, the well-known 
Paris Microscope maker, and it also contains some beautiful and rare 
instruments. Among others he has a unique specimen of the first known 
* Amer. Mon. Micr. Journ., xiv. (1893) pp. 15-6. 
