iv CONTENTS. 



PAGE 



73. Change of position of constellations. 74. Zodiac. 75. 

 Ecliptic. 76. Other contents of Almanack. 77. Astronomical 

 terms. 78. Conjunction. 79. Opposition. 80. Quadratures. 

 81. Morning and evening star. 82. Further illustrations. 

 83. Lunar changes. 84. When said to.be gibbous . . .33 



CHAP. IV. 85. Full moon. 86. Last quarter. 87. Moon's age. 88. 

 Eate of motion variable. 89. Causes thereof. 90. "May moon," 

 "March moon," &c. 91. Confusion arising from this form of 

 expression. 92. The epochs of chronology. 93. Anno Mundi. 

 94. Era of Nabonassar. 95. The Hegira .... 49 



COMMON THINGS COLOUR. 



CHAP. I. 1. Colours depend upon reflected lights. 2. Bodies lumin- 

 ous and non-luminous. 3. Luminaries. 4. Non-luminous bodies. 

 5. Transparency and opacity. 6. Transparency never perfect. 

 7. Opacity never perfect. 8. Bodies rendered visible by reflected 

 light. 9. Irregular reflection. 10. Reflecting powers vary. 

 11. The blackest body reflects some light. 12. Irregular reflec- 

 tion necessary to vision. 13. Use of the atmosphere in diffusing 

 light 57 



CHAP. II. 14. Diffusion of light by all visible objects. 15. Decom- 

 position of light by visible objects. 16. Experimental proof of 

 the composition of light. 17. The prismatic spectrum. 18. The 

 composition of solar light 19. The recomposition of light by 

 prism. and concave reflector. 20. The same by prism and lens. 

 21. The same with artificial colours. 22. Light of the same 

 colour may have different refrangibilities. 23. Colours produced 

 by combining different rays of the spectrum. 24. Comple- 

 mentary colours. 25. Colours of natural bodies generally 

 compound. 26. Method of observing the spectrum by direct 

 vision. 27. Why objects seen through prism are fringed with 

 colours. 28. The prismatic colours, not all simple. 29. Sir D. 

 Brewster's analysis of the spectrum ..... 65 



OPTICAL IMAGES. 



CHAP. I. 1. Great importance of the subject in relation to all the 

 effects of vision. 2. Explanation of how an object is seen with 

 the naked eye. 3. Images produced by plane reflectors. 

 4. How rays are reflected 'from such surfaces. 5. Experimental 

 verifications of this. 6. Image of a point in a plane reflecting 

 surface. 7. Image of an object in the same. 8. Real and 

 imaginary images. 9. Images produced by spherical reflectors. 

 10. By a concave reflector. 11. Experimental verification. 

 12. Variation of position, and magnitude of image. 13. Images 

 in convex reflectors. 14. Images produced by transparent bodies. 

 15. Refraction. 16. Cases in which light will not enter a 

 transparent body. 17. Reflection of objects in water. 18. The 



