PREFACE TO THE THIRD EDITION. 



In presenting to the public this edition, the Author 

 deems it proper to remark that he has retained the same 

 mechanical construction of the Microscope as appeared in 

 the preceding edition. It is more especially necessary to 

 mention this circumstance, inasmuch as of late some very 

 elaborately constructed Microscope-stands have been made 

 by different opticians, which, though they deserve high 

 commendation, both on account of the ingenuity displayed 

 in the details of their construction, and the exquisite finish 

 of their workmanship, still, from their great costliness, their 

 adding little to the efficiency of the optical part of the 

 instrument, and no two makers having adopted the same 

 form, they are not likely to come into very general use. 

 For these reasons the original forms are here retained. 



The essential principles of construction are explained 

 in the work, and it must be borne in mind that the in- 

 structions for the use and management of Microscopes 

 herein given apply in most cases to all, however varied in 

 form. 



The valuable memoirs of Dr. Goring, which appeared 

 in the " Microscopic Cabinet," are given in this edition by 

 way of supplement. This course appeared desirable as 

 that work is out of print, and the natural history portion 

 is now published separate, under the title of "Notes on 

 Natural History" 



The concluding paragraph relative to these Memoirs is 

 extracted from the preface to the " Cabinet. 5 ' Its accuracy 

 has been verified by the fact, that not a single maker of 

 Microscopes now exists (at least in this country) who 

 fabricated Achromatic Object-glasses prior to its pub- 



