SIMPLE MICROSCOPES. 



b protects the eye from the light by which the object is illu- 

 minated, an arm e is jointed at d, so that it can be turned flat 

 against , when the instrument is not in use, and can be inclined 

 to a, at any desired angle. This arm being round, a sliding 

 tube/ is placed upon it, fixed to another tube at right angles to 

 it, in which a vertical rod slides, to the upper end of which is 

 attached a forceps or any other convenient support of the object 

 under examination. 



Several doublets or triplets of various powers may be provided, 

 any of which may be inserted at pleasure in the socket c. 



32. When still greater steadiness is required, and greater bulk 

 and higher price do not form an objection, the arm and socket 

 bearing the doublet are fixed upon a vertical pillar, screwed to a 

 table with proper accessories for adjusting the focus and illumi- 

 nating the object. 



The arrangement adopted in the simple microscopes of Charles 

 Chevalier, shown in fig. 15, p. 97, may be taken as a general 

 example of this class of mounting. 



The case in which the instrument is packed serves for its 

 support when in use. A square brass pillar T T, screwed into the 

 top of this case x, has a square groove cut along one of its sides, 

 in which the square rod G is moved upwards and downwards by 

 a rack and pinion E ; at the top of this rod, a horizontal arm a is 

 attached, at the end of which a socket is provided to receive the 

 doublets ; several of which having different powers are supplied 

 with the instrument. 



The object under observation is supported on the stage p, 

 firmly attached to the upper end of the square pillar T T ; in this 

 stage is a central hole, through which light is projected on its 

 lower surface when the object is transparent, and the quantity of 

 this light is modified by means of an opaque disc D, pierced with 

 holes of different magnitudes. 



By turning this disc on its centre, any one of these holes may 

 be brought under the object ; when the object is not transparent, 

 the opening in the stage is stopped, and it is viewed by light 

 thrown upon its upper surface. 



A square box E, sliding upon the pillar T T, with sufficient fric- 

 tion to maintain it at any height at which it is placed, carries a 

 reflector M, by which light is projected upwards to the opening of 

 the stage p, this light being more or less limited in quantity by 

 the orifice of the diaphragm D, which is presented in its path. 

 t In this instrument the object is brought into focus by moving 

 the arm which carries the doublet up and down, by means of the 

 rack and pinion K, the stage supporting the object being fixed. 

 The same effect might be, and is in some microscopes, produced 



111 



