COMPOUND MICROSCOPE. 



109 



In the Compound Microscope the 

 imagre is inverted, the field of view is 

 small, the illumination or light coming 

 from the object is diminished, nnd the 

 maguification is much increased. 



The parts of a Compound Microscope 

 may be conveniently divided into two 

 groups, the mechnnioal and the optical. 

 A reference to the accompanying illus- 

 tration will serve to locate the parts 

 named and described. 



The mechanical parts are the base, or 

 foot; the pillar, below stage and above 

 stage, with a hinge joint between; tube, 

 or body; draw tube; rack and pinion, or 

 coarse adjustment; micrometer screw, or 

 fine adjustment; stage; nose-piece; stage 

 clips; diaphragm; mirror bar; sub-stage, 

 if present. 



The optica! parts are oculars, or eye- 

 pieces; objectives; mirror; condenser. 



The Mechanical parts or parts of the 

 Stand proper. 



The Ba?;e or Foot is that part which 

 supports the microscope. It is made in 

 various shapes, triangular, circular or 

 horse-shoe. It should be firm, and heavy 

 enough to allow the microscope to be 

 tilted upon its axis and still stand 

 steady. 



It bears the Pillar, which has a por- 

 tion below and above the stage, which is 

 broken by a hinge joint (not always pres- 

 ent), which allows the microscope to be 

 inclined at any angle. 



To the pillar is attached the Stage and 

 the Arm, The Stage is gen^-ally round 

 or square, and should be firm, flat, and 

 large, at least four inches across. It is 

 perforated at the centre by an aperture, 

 which allows the light to pass through it 

 to illuminate the object. It also has a 

 pair of Clips to hold the glass slide in 

 place. 



The Arm bears the Body or Tube. A 

 firm arm is an essential to a good mi- 

 croscope. 



The Body or Tube is attached to the 

 arm by means of a Rack and Pinion 

 piece. This is called the Coarse Adjust- 

 ment, and permits t]}e tube to be lowered 

 or raised. The Fine Adjustment con- 

 sists of a micrometer screw situated at 

 the top of the pillar. 



The Tube frequently has a draw tube, 

 into the upper end of which the Ocular 

 or Eye-piece is set. To the lower end 

 of the tube the Objectives are attached. 



In most modern instruments there is 

 added an especial apparatus called the 

 Nose-piece, to which two or more ob- 

 jectives may be attached, any one of 

 which may thus be brought into position. 

 • Below the stage there may be Sub- 

 Stage, which may be provided with a 

 Condenser, the Abb6 being the best. 

 From the lower portion of the stage near 

 the pillar the Mirror Bar descends, car- 



Fig. 3. Iris Diaphragm, 



rying the Mirror, and in some instances 

 a Diaphragm. In some instruments the 

 diaphragm is situated just below the 

 aperture, and may be of several types; 

 the most useful one is the Iris Dia- 

 phragm, as displayed in the cut. 



In the best of modern instruments the 

 whole sub-stage arrangements are bound 

 together in one mechanism, as in Fig. 4. 



The Optical Parts: 



The Ocular or Eye-Piece is set into 

 the upper portion of the tube. There 

 are two types of eye-pieces, the negative, 

 or Huyghcnian, which is the more com- 

 monly used, and the positive, or Rams- 

 den, now rarely seen in microscopic use. 

 In the more advanced types of instru- 

 ments there is the so-called compensat- 

 ing ocular, which is, however, only used 

 with the newer apochromatic objectives* 



The action of the eye-piece is that of 

 a simple magnifier, but it magnifies the 

 real image which the objective produces, 

 as if that image were the original ob- 

 ject. 



Oculars are designated as high and 



low, and are measured in inches or milli- 

 meters; the longer the ocular, the lower 

 or weaker it is in -magnifying power, and 

 vice-versa. (Fig. 5.) 



The Objective is often called the most 

 important part of the instrument, which 

 is, in many senses, true, for the great 

 advances that have come about in the 

 biological sciences have been mainly due 



