1893. SOME NEW BOOKS. 465 
of what is indispensable in a thoroughly good and practical camera — 
always in both cases keeping the specific object which is sought in 
view. 
It is true that Dr. Van Heurck nas presented us with a very 
attractive model of a microscope for ‘‘ the study and photography of 
Diatoms, and all delicate researches,” but the model has not many 
new or specially advantageous features when considered as one of the 
many English models before the public. It has, as we think, in 
common with some of the very finest English workers, some distinct 
disadvantages; but it certainly overcomes the difficulty of the 
working of the fine adjustment on good conditions better than any 
instrument that we know of the Jackson model (which is in practice 
an inferior form) that adopts similar methods. The fine adjustment 
is delicate, and the instrument is throughout supplied with admirable 
facilities for accuracy and ease in use. Hundreds of skilled workers 
would refuse it at once as representing the best possible form of a 
modern microscope; but much has been done to soften the evils 
inherent in the form. Yet all these are costly, and when they are 
effected we are bound to submit that it is not the best form of the 
instrument that is either possible or accessible; and, above all, it is 
not the best form of the instrument that can be constructed at a low 
expenditure. 
The amateur wants a useful, well-made instrument at a low cost. 
So does the medical student. What, therefore, is essential to a good 
microscope in any form? What form of stand has the largest 
number of points in its favour, practically considered ? and which 
are the stands of the modern makers, English, Continental, or 
American, that, at a moderate cost, most largely meet these require- 
ments ?—these are the considerations which are of the greatest value 
to the purchasers of modern handbooks, from this side of the subject, 
and its efficient discussion would involve a consideration of that most 
practical of all questions in such a treatise, the relative values of the 
English as against the Continental stands, or vice versa; but this is 
wholly avoided. 
There is one other point which we desire to touch but lightly, it 
is that here and there in the book phraseology has been adopted that 
certainly does not represent, if it does not absolutely run counter to, 
the diffraction theory of microscopic vision. It is not necessary to 
dwell on this; probably it may in some instances be inadvertence ; 
but in a treatise intended to teach ab initio the doctrines of Abbe on 
the optics of the modern microscope, especially as there is some ob- 
scurity in the inculcation of these, it is unfortunate to find incidental 
passages that imply not only complications but contradictions. 
The translator’s work has manifestly been done with care and 
sincerity, and most fairly presents the meaning of the author; and 
the book, though large and heavy for use at the work-table, is 
unusually good. 
There are many points of excellence in the work, and some that 
give evidence of the practical skill of the author; indeed we can see 
the possibility in a second and greatly revised edition of a book of 
high quality and usefulness ; but it will involve the excision of much 
that is now useless in its pages, and the rendering useful by ample 
and lucid preface and explanation of much in it that, although 
useful in itself, is doubtfully, if at all, useful in the form and 
relations in which it is presented to the enquirer in the book as it 
now stands. 
2H 
