CHAPTER I 

 THE MICROSCOPE AND ITS PARTS 



§ 1. Apparatus and material for Chapter I. 



1. A simple microscope (§ 3, 14, 6. Stage micrometer (§ 48). 



fig. 4, 6). 7. Homogeneous immersion liquid 



2. A compound microscope with (§ 25). 



nose-piece (§4, fig. 25-28). 8. Mounted letters or figures (§ so). 



3. Eye-shade (fig. 33). 9. Ground-glass and lens paper 



4. Achromatic (§. 26), apochro- (§ 50). 



matic (§ 28), dry (§ 22), immersion 10. Black card with pin-hole (§ 7, 



(§ 23-25), unadjustable (§ 30), ad- fig. 7). 



justable objectives (§ 31). 11. Dissecting spectacles (§ 14s). 



5. Huygenian or negative (§ 38), 

 positive (§ 39), compensation ocu- 

 lars (§40). 



§ 2. As the word itself indicates, a microscope is an instrument 

 with which one can see small things (§ 2a). 



The microscope makes small things or minute details of larger 

 things visible in two distinct ways, both ways being dependent on an 

 increase of the visual angle (§ 6, 226-227, ^g- 7S~76)- 



(i) The first way of increasing the visual angle and thus making 

 small things or details visible is by means of one or more lenses used 

 as a kind of spectacle by which the eye is enabled to form a sharp 

 image on the retina when optically so close to the object that with- 

 out the artificial aid a sharp image on the retina could not be pro- 

 duced (fig. 2, 3, 6). 



(2) The second way of increasing the visual angle under which 

 small things or details are viewed is by means of a projection micro- 

 scope, which, wholly independent of the eye, produces a sharp, greatly 

 enlarged image of the object upon a white surface. The eye then 

 looks at this image as though it were the object itself and of that size 

 (fig. I, § 312). 



The fundamental difference in the two forms of microscope is that 



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