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 has 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 a^■oided. 



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. 



