LIST OF ILLUSTRATIONS.

PAGE

1. Refraction of Parallel Rays by Plano-convex Lens,

2.

Ditto

3. Refraction of Converging Rays,

4. Refraction of Diverging Rays,

5. Formation of Images by Convex Lenses,

6. Spherical Aberration,

7. Chromatic Aberration,

8. Section of the Achromatic Object-glass,

9. Effect of Covering-glass,

10. Action of Simple Microscope,

11. Simplest form of Compound Microscope,

12. Complete Compound Microscope,
13. Huyghenian Eye-piece,.
14. Ross's Simple Microscope,
15. Gairdner's Simple Microscope,
16. Field's Simple Microscope,
17. Quekett's Dissecting Microscope,
18. Field's Compound Microscope,
19. Highley's Hospital Microscope,
20. Nachet's Compound Microscope,
21. Smith and Beck's Student's Microscope,

22.

Ditto

67

by Double-convex Lens,

67

68

68

70

70

72

75

76

78

82

82

83

91

92

23. Warington's Universal Microscope,

105

24.

Ditto

Ditto,

106

Ditto,

95. Grammatophora serpentina, after Smith,

77. Didymoprium Grevillii, after Ralfs,

78. Portion of Isthmia nervosa, after Smith,
79. Triceratium favus, after Smith,

80. Pleurosigma angulatum, after Wenham,
81. Biddulphia pulchella, after Smith,
82. Conjugation of Epithemia, after Thwaites,
83. Conjugation of Aulacoseira, after Thwaites,
84. Actinocyclus undulatus, after Smith,
85. Heliopelta,

86. Arachnoidiscus Ehrenbergii, after Smith,
87. Campylodiscus costatus, after Smith,
88. Surirella constricta, after Smith,
89. Gomphonema geminatum, after Smith,
90.

91. Licmophora flabellata, after Smith,

93. Achnanthes longipes, after Smith,

94. Diatoma vulgare, after Smith,

96. Isthmia nervosa, after Smith,

97. Meloseira subflexilis, after Smith,

275

280

281

282

283

285

286

289

290

291

292

293

294

more highly magnified, after Smith,

295

296

92. Meridion circulare and Bacillaria paradoxa, after Smith,

296

297

298

298

298

299

102. Fossil Diatomacea from Mourne Mountain, after Ehrenberg,