48, 49, 50. Manner in which the rays of light are refracted in telescopes. 231 51. Telescope with a single lens. 234 52. Illustrative of spherical aberration 236 53. Illustrative of the principle of achromatic telescopes. 241 54, 55. Double and treble achromatic object-glass. 242 57. Common stand for achromatic telescopes. 260 58. Equatorial stand for achromatic telescopes. 262 59. Dollond’s stand for achromatic telescopes. 264 60. Blair’s fluid achromatic object-glass. 271 61. Barlow’s fluid telescope. 274 62, 63, 64, 65, 66. Various forms of reflecting telescopes. 288 67. Gregorian reflecting telescope. 293 69. The aerial reflector. 313 70. Front view of the aerial reflector. 314 71. Construction of large reflecting telescope 322 72. Reflecting telescope with a single mirror 332 73. Huygenian eye-piece. 336 74. Ramsden’s eye-piece. 339 75, 76. Combination of lenses for achromatic eye-pieces. 340 77, 78. Diagonal eye-pieces. 344, 345 79. Terrestrial eye-piece with four lenses. 349 80. Eye-piece of an old Dutch achromatic telescope. 356 81. Pancratic eye-piece. 359 82. Manner of exhibiting the solar spots. 384 84. Mode of measuring distances from one station. 430 85. Cavallo’s micrometer. 446 86. The equatorial telescope, or portable observatory. 455 87. Figure to illustrate the principle of the quadrant. 491 88. The astronomical quadrant. 493 89. The astronomical circle. 496 90. The transit instrument. 502 91. Plan of a private observatory. 511 92. Rotatory dome for an observatory. 513 93. Wheel-work of a planetarium. 521 94. Perspective view of a planetarium. 522 95. Apparatus for exhibiting the retrograde motions of the planets. 525 96. Section of the wheel-work of Dr. Henderson’s planetarium. 528 97. Thirteen views of the supposed form of Saturn’s ring. 539