42 THE MICROSCOPE AND ITS REVELATIONS. 



too trivial to deserve mention; but no practised Microscopist will be slow 

 to acknowledge their value. For other purposes, again, it is requisite 

 that the Microscope should be placed horizontally, as when the Camera 

 Lucida is used for drawing or measuring. It ought, therefore, to be 

 made capable of every such variety of position; and the Stage must of 

 course be provided with some means of holding the object, when it is 

 itself placed in a position so inclined that the object would slip down 

 unless sustained. 



iv. The last principle on which we shall here dwell, as essential to the 

 value of a Microscope designed for ordinary work, is Simplicity in the 

 construction and adjustment of every part. Many ingenious mechanical 

 devices have been invented and executed, for the purpose of overcoming 

 difficulties which are in themselves really trivial. A moderate amount 

 of dexterity in the use of the hands is sufficient to render most of these 

 superfluous; and without such dexterity, no one even with the most com- 

 plete mechanical facilities, will ever become a good Microscopist. Among 

 the conveniences of simplicity, the practised Microscopist will not fail to 

 recognize the saving of time effected by being able quickly to set up and 

 put away his instrument. Where a number of parts are to be screwed 

 together before it can be brought into use, interesting objects (as well as 

 time) are not unfrequently lost; and the same cause will often occasion 

 the instrument to be left exposed to the air and dust, to its great detri- 

 ment, because time is required to put it away; so that a slight advantage 

 on the side of simplicity of arrangement often causes an inferior instru- 

 ment to be preferred by the working Microscopist to a superior one. Yet 

 there is, of course, a limit to this simplification; and no arrangement can 

 be objected-to on this score, which gives advantages in the examination 

 of difficult objects, or in the determination of doubtful questions, such as 

 no simpler means can afford. The meaning of this distinction will be- 

 come apparent, if it be applied to the cases of the Mechanical Stage and 

 the Achromatic Condenser. For although the Mechanical Stage many 

 be considered a valuable aid in observation, as facilitating the finding of 

 a minute object, or the examimation of the entire surface of a large one, 

 yet it adds nothing to the clearness of our view of either; and its place 

 may in great degree be supplied by the fingers of a good manipulator. 

 On the other hand, the use of the Achromatic Condenser not only con- 

 tributes very materially, but is absolutely indispensable, to the formation 

 of a perfect image, in the case of many objects of a difficult class: the want 

 of it cannot be compensated by the most dexterous use of the ordinary 

 appliances; and consequently, although it may fairly be considered super- 

 fluous as regards a large proportion of the purposes to which the Microscope 

 is directed, whether for investigation or for display, yet as regards the 

 particular objects just alluded to, it must be considered as no less neces- 

 sary a part of the instrument than the Achromatic Objective itself. 

 Where expense is not an object, the Microscope should doubtless be fitted 

 with both these valuable accessories; where, on the other hand, the cost 

 is so limited that only one can be afforded, that one should be selected 

 which will make the instrument most useful for the purposes to which it 

 is likely to be applied. 



In the account now to be given of the principal forms of Microscope 

 readily procurable in this country, it will be the Author's object, not so 

 much to enumerate and describe the various patterns which the several 



