00 CONSTRUCTION OF THE MICROSCOPE. 



m. Scarcely less important than the preceding requisite, in 

 the case of the Compound Microscope, though it does not add 

 much to t&e utility of the Simple, is the capability of being placed 

 in either a vertical or a horizontal position, or at any angle with the 

 horizon, without deranging the adjustment of its parts to each 

 other, and without placing the eye-piece in such a position as to 

 he inconvenient to the observer. It is certainly a matter of sur- 

 prise, that Opticians, especially on the Continent, should have 

 so long neglected the very simple means which are at present 

 commonly employed in this country, of giving an inclined posi- 

 tion to microscopes ; since it is now universally acknowledged, 

 that the vertical position is, of all that can be adopted, the very 

 worst. An inclination of about 55° to the horizon will generally 

 be found most convenient for unconstrained observation ; and 

 the instrument should be so constructed, as, when thus inclined, 

 to give to the stage such an elevation above the table, that when 

 the hands are employed at it, the arms may rest conveniently 

 upon the table. In this manner a degree of support is attained, 

 which gives such free play to the muscles of the hands, that 

 movements of the greatest nicety may be executed by them ; 

 and fatigue of long-continued observation is greatly diminished. 

 Such minutiae may appear too trivial to deserve mention ; but 

 no practised microscopist will be slow to acknowledge their value. 

 The stage must of course be provided with some means of sup- 

 porting the object, when it is itself placed in a position so in- 

 clined that the object would slip down unless sustained. There 

 are some objects, howevei', which can only be seen in a vertical 

 microscope, as they require to be viewed in a position nearly or 

 entirely horizontal ; such are dissections in water, urinary de- 

 posits, saline solutions undergoing crystallization, &c. For other 

 purposes, again, 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. 



TV". The last principle on which we shall here dwell, is simpli- 

 city in the construction and adjustment of every part. Many in- 

 genious mechanical devices have been invented and executed, 

 for the purpose of overcoming difficulties which are in them- 

 selves 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 complete 

 mechanical facilities, will ever become a good microscopist. 

 Among the conveniences of simplicity, the practised Microsco- 

 pist will not fail to recognize the saving of time effected by being 



" lose time ;" whilst its delicacy and smoothness admit of an exact adjustment being 

 made by its means alone, even when high powers are employed. Still, as will be shown 

 hereafter (§ 81), the use of the "fine adjustment" is by no means restricted to this pur- 

 pose ; and it cannot be advantageously dispensed with in a Microscope, which is to be 

 used for any but the most common purposes. 



