175 



publication of the Journal as to preclude a notice of the length that 

 its merits deserve. The optical part is written so clearly and 

 without any parade of imposing mathematical formulas, except 

 where such are imperative or easily understood, that, instead of 

 causing weariness, as is generally the case, it is a pleasure to read. 

 The properties of lenses, the images formed by single and com- 

 bined systems, angular and numerical aperture, aberration and the 

 whole theory of secondary images, are all treated in a masterly 

 way. The various details of the microscope, particularly the 

 objectives and eyepieces, their construction and action, are 

 exhaustively and practically described, but if it is allowable to 

 indicate, from onr point of view of course, one little blemish 

 where nearly everything is excellent it is in the matter of the sub- 

 stage condenser. Abbe's chromatic is the only apparatus of the 

 kind mentioned, and it appears strange to us that, while the 

 aperture of the objective is treated with such scientific insight 

 and its value so thoroughly grasped, the equally important factor 

 of the illumination is yoked to such a comparatively inefficient 

 means of utilizing such aperture as is afforded by this widely-used 

 but optically unsound condenser. Nevertheless, it must not be 

 forgotten that Dr. Zimmermann is writing for German readers, 

 and that up to quite recently they universally regarded the sub- 

 stage condenser as a mere English ' fad,' so if they are content 

 for the time with an inferior form it is still an advance on their 

 former attitude, and we must not complain. 



So far as we have had time to judge the practical portion of the 

 book is equally good and to the point as the more theoretical, 

 while space has not been wasted on a host of staining and chemical 

 processes, which can easily be found elsewhere. It concludes with 

 a chapter on Microscopical perception, dealing with the images 

 given by an opaque reflecting sphere, as a globule of quicksilver, 

 an air bubble, and a drop of oil in water. There is a short biblio- 

 graphy and index. For such microscopists as read German, and 

 particularly those that employ German instruments, the work will 

 be of very considerable service. 



A Popular Handbook to the Microscope. By Lewis 

 Wright. The Eeligious Tract Society. 2s. 6d. 



This excellent work, which contains 256 pages, two plates, and 

 186 woodcuts in the text, can be strongly recommended to the 

 rank and file of the ever-increasing army of microscopists as well 



