APPENDIX. 29? 



LESSON 34. 



Fig. 37. P is a prism. A is a ray of light, which is re- 

 fracted on entering the prism, and also on leaving it. A B 

 is the spectrum, on which are exhibited the variously colour- 

 ed rays. 



LESSON 36. 



Structure of the Eye. Fig. 28. aaaaa, is called the 

 sclerotica : h b, the cornea : c cc, the choroid : d d, the pu- 

 pil : e e, the iris : ff, the aqueous humour : g g, the cri/s- 

 talline humour : h h, the vitreous humour : i i, the retina ; 

 which proceeds from the brain and enters the eye at n. 



LESSON 37. 



Single Microscope, Jig. 35. E F is the object to be view* 

 ed : A B a double convex lens : c the pupil of the eye : D 

 the crystalline humour : the rays are converged to a focus on 

 the retina at R R. Compound Microscope, Jig. 34. with 

 which we do not see the object A B, but a magnified image 

 of it a h. Two lenses are employed ; the one L M, for the 

 purpose of magnifying the object, is called the object glass : 

 the other N O, acts on the principle of the single micro- 

 scope, and is called the eye glass. 



LESSON 39. 



To obtain an idea of the Newtonian Telescope, look at 

 jig. 27. ai»d consider the concave mirror A B as placed at 

 the end of a tube, and rays of light falling upon it from the 

 object DE : then suppose a plane mirror placed a little be- 

 low e, so that the rays, being reflected from it, shall pass out 

 through a lens at d, where the eye of the observer looks 

 down on the image. 



LESSON 4L 



Solar System. Engr. IV. Fig. 38 exhibits the order in 

 which the planets move round the sun. Fig. 39 shows 

 their comparative magnitudes. On the left hand side of the 

 Engr. are represented the proportional distances of the 

 olanets from the sun. 



