OUR BOOK SHELF, 267 
deemed inadvisable—at least at present—to trouble the reader with 
too much theory, and the little that has been said upon the subject 
of Microscopical definition, it is hoped is sufficiently lucid. 
The author has not fought shy of the “angle” question. He 
recommends moderate angles for general work, because such 
objectives have long working distances and can be employed with- 
out any trouble ; but where excellent definition is required, none 
but the widest apertures should be used. 
In chapter II. is to be found a table of the magnifying powers of 
English objectives, and also similar ones of those of Messrs. Zeiss 
and Hartnack, which may be useful as a means of comparison of 
the work done with English and Foreign glasses. 
Chapter V. has been written with the view of aiding students in 
the manner of illuminating their subjects, for it is a matter patent 
to experts, that with beginners the chief errors arise through bad 
illumination, and even older Microscopists are often at sea in this 
respect. It is astonishing how much may be done with the bull’s-eye 
condenser alone, yet students as a rule are not aware of it. The 
various qualities of objectives are treated of in this chapter : Work- 
ing distance—Defining power—Flatness of field—Penetration— 
Resolving power; and the author in his arguments has endeavoured 
not to be wearisome. Most of the “Test objects ” mentioned are 
illustrated, many of them being photographed from nature. 
The chapter on the collection of objects is amplified by a list 
of works treating upon each special subject, while the names of 
several objects in each class have been given to fix, if possible, the 
attention of the beginner in some definite groove. Most of these 
works may be obtained at the Free Libraries, which now are 
situated in many large towns. 
The chapters on Dissecting and Section cutting have been made 
as practical as possible, ample instructions having been given for 
the cutting of animal, vegetable, and mineral sections, with the aid 
of inexpensive apparatus. 
Chapter IX. contains directions for the delineation of objects by 
several means, ruled squares, neutral tint reflector, camera lucida, 
while the greater portion is taken up with a full description of the 
art of photo-micrography. ‘This subject is treated of in all its de- 
tails, the chemical portion being fully explained, including the 
preparation of transparencies for the lantern. 
Chapters X. and XI. treat of the Polariscope and of the Micro- 
spectroscope, while chapter XII. thoroughly explains the art of 
staining and injecting. In order to thoroughly set forth the advant- 
ages of double staining, the frontispiece has been prepared, which 
we give as a plate to accompany this number, the four outside 
figures, representing four of Mr. Ward’s double stained wood- 
sections (as advertised on the cover); the centre figure being a 
