INTRODUCTION. 



XI 



and properties of objects in general is of more importance than may at first be apparent ; 

 for bodies as found in nature are generally of a mixed kind, and it too often happens that a 

 young observer, soon after having procured a microscope, takes up some particular line of 

 investigation, to which he may have been previously attracted; and without the least 

 knowledge of the structure of objects in general, of what has been done before or of the 

 proper method of using the instrument, he arrives at the conclusion that all is new and 

 satisfactory. The whole is then destined to encumber the pages of scientific works with 

 a load of imperfect and useless details. 



But, independently of the disadvantages attendant upon the improper use of the micro- 

 scope, there are difficulties inherently connected with the examination of microscopic objects, 

 which are not encountered when objects are examined with the naked eye. One of these 

 is, that with flie ordinary microscope, objects are only viewed with one eye ; hence we lose 

 the direct power of distinguishing solidity, &c., and are compelled to resort to indirect 

 means for these purposes. This difficulty is however now being overcome, since stereoscopic 

 microscopes are being constructed, and although not yet brought to perfection, will 

 undoubtedly be so in a short time. The ordinary objects around us are also usually viewed 

 by reflected light, whilst with the microscope they are mostly viewed by transmitted light, 

 and we are consequently much less practised in judging from the appearances of objects 

 thus illuminated, and therefore liable to err. 



Another, but a less important difficulty in microscopic investigations, or at least manipu- 

 lations, consists in the image of the objects being inverted. Erecting eyepieces, as they 

 are called, will obviate this difficulty ; but as they are expensive, they are seldom used. 



Another very serious source of error lies in the tendency to reason from analogy, as to the 

 structure or nature of a body viewed under the microscope. Any one who pursues this 

 course, has his mind prejudiced by preconceived notions, and becomes in fact no observer 

 at all. 



In regard, again, to the real utility of the microscope, the time has passed when this might 

 be called in question ; it must be universally acknowledged by those who are in search of 

 truth in regard to the subjects it is employed to investigate. It need, moreover, be merely 

 remarked, that the ordinary appearance of objects to the naked eye, depends in all cases 

 upon a molecular structure, which is generally microscopic, the ordinary appearance being 

 the optical result or expression of this structure, and since totally dissimilar microscopic 

 structures may present similar appearances to the unaided eye, judgment as to the nature 

 of the former founded upon the latter can be of but little value. The reader will remember 

 that the common capability of distinguishing objects or structures by their appearance, 

 has been derived from practice and experience of effects ; when we bear in mind that the 

 experience and practice in the study of the causes are attainable, the superiority of the latter 

 must be evident. 



Above all, however, it must never be forgotten, that microscopic investigations require 

 more time and patience than perhaps any others, even in regard to the determination of 

 simple facts of structure and qualitative composition ; and although it is not very uncommon 

 still to hear those engaged in them sneered at as wasting their time over a very simple 

 plaything, this may be regarded as arising from one of those prejudices which will exist so 

 long as people will venture to express opinions upon matters with which they are unac- 

 quainted, and which are beyond their comprehension. 



We have expressed our intention of not entering upon a description of the microscope as 

 an optical instrument, and this, because it would have been requisite to have trodden widely 

 the field of general optics, which our space would not permit. We would advise, then, 

 those who wish to become acquainted with the microscope as an optical instrument, first to 



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