Fig. 1. 



Fig. 3. 



Fig. 4. 



PLATE I. 



Negative or Huy^benian. 

 eye-piece, p. 5. 



Positive eye-piece, invented 

 by Ramsden. p. 5. 



Fig. 5. 



Diagram of compound microscope. 

 A, point where tbe object is brought 



A, point wnere me onject is uruuguii 

 to a focus by tbe object glass, C. The 

 image formed at this point is mag- 

 nified again by the eye-piece, B p 4. 



To illustrate ' chromatic aberration.' The violet and blue rays being moat 

 refrangible are brought to a focus. A. nearer the lena than the red rays, T. 

 which are the least refrangible of the rays of the spectrum ; any object placed 

 at LL would exhibit coloured fringes, p 6. 



Fig. 6. 



Diagram of simple microscope, p. 4. 



Fig. 9. 



To illustrate 'spherical aberration.' The rays, A A, 



being more refracted than those near the centre, B, 



are brought to a focus nearer the lens. p. ti. 



Fig. 8. 



Compound glasses of 



an achromatic object 



glass, p. 5. 



Stage of student's microscope, showing diaphragm 



placed beneath. From a to 6 should not be less 



than two inches, p. 9. 



a. objective with low angle of aperture, BAB 

 6, another with high angle of aperture BAB 



P- " 



[To face page 8. 



