BOOK VI.
ASTRONOMICAL PHYSICS.
XXV.— THE GENERAL FIELD OF PHYSICAL INQUIRY 371
XXVI.— DETERMINATION OF THE LIGHT AND HEAT OF THE STARS 377
XXVII.— THE CHEMISTRY OF THE STARS: CONSTRUCTION OF THE 386 SPECTROSCOPE
XXVIII.— THE CHEMISTRY OF THE STARS (CONTINUED): PRINCIPLES OF 401 SPECTRUM ANALYSIS
XXIX.— THE CHEMISTRY OF THE STARS (CONTINUED): THE 422 TELESPECTROSCOPE
XXX.— THE TELEPOLARISCOPE 441
XXXI.— CELESTIAL PHOTOGRAPHY.—THE WAYS AND MEANS 454
XXXII.— CELESTIAL PHOTOGRAPHY (CONTINUED): SOME RESULTS 463
XXXIII.— CELESTIAL PHOTOGRAPHY (CONTINUED): RECENT RESULTS 469
LIST OF ILLUSTRATIONS.
FIG. PAGE
1. The heavens according to Ptolemy 3
2. The zodiac of Denderah 7
3. Illustration of Euclid’s statements 10
4. The plane of the ecliptic 13
5. The plane of the ecliptic, showing the inclination of the 14 earth’s axis
6. The first meridian circle 20
7. The first instrument graduated into 360° (west side) 21
8. Astrolabe (armillæ æquatoriæ of Tycho Brahe) similar to the 26 one contrived by Hipparchus
9. Ecliptic astrolabe (the armillæ zodiacales of Tycho Brahe), 28 similar to the one used by Hipparchus
10. Diagram illustrating the precession of the equinoxes 31
11. Revolution of the pole of the equator round the pole of the 32 ecliptic caused by the precession of the equinoxes
12. The vernal equinox among the constellations, B.C. 2170 34
13. Showing how the vernal equinox has now passed from Taurus and 34 Aries
14. Instrument for measuring altitudes 35
15. Portrait of Tycho Brahe (from original painting in the 39 possession of Dr. Crompton, of Manchester)
16. Tycho Brahe’s observatory on the island of Huen 43
17. Tycho Brahe’s system 46
18. The quadrans maximus reproduced from Tycho’s plate 48
19. Tycho’s sextant 50
20. View and section of a prism 56
21. Deviation of light in passing at various incidences through 57 prisms of various angles
22. Convergence of light by two prisms base to base 59
23. Formation of a lens from sections of prisms 60
24. Front view and section of a double convex lens 61
25. Double concave, plane concave, and concavo-convex lenses 61
26. Double convex, plane convex, and concavo-convex lenses 62
27. Convergence of rays by convex lens to principal focus 62
28. Conjugate foci of convex lens 63
29. Conjugate images 64
30. Diagram explaining Fig. 29 64
31. Dispersion of rays by a double concave lens 65
32. Horizontal section of the eyeball 66
33. Action of eye in formation of images 68
34. Action of a long-sighted eye 69
35. Diagram showing path of rays when viewing an object at an 70 easy distance
36. Action of short-sighted eye 71
37. Galilean telescope 73
38. Telescope 75
39. Diagram explaining the magnifying power of object-glass 76
40. Scheiner’s telescope 78
41. Dispersion of light by prism 80
42. Diagram showing the amount of colour produced by a lens 81
43. Decomposition and recomposition of light by two prisms 83
44. Diagram explaining the formation of an achromatic lens 84
45. Combination of flint- and crown-glass lenses in an achromatic 86 lens
46. Diagram illustrating the irrationality of the spectrum 87
47. Diagram illustrating the action of a reflecting surface 91
48. Experimental proof that the angle of incidence = angle of 92 reflection
49. Convergence of light by concave mirror 94
50. Conjugate foci of convex mirror 94
51. Formation of image of candle by reflection 95
52. Diagram explaining Fig. 51 96
53. Reflection of rays by convex mirror 98
54. Reflecting telescope (Gregorian) 101
55. Newton’s telescope 102
56. Reflecting telescope (Cassegrain) 103
57. Front view telescope (Herschel) 103
58. Diagram illustrating spherical aberration 105
59. Diagram showing the proper form of reflector to be an ellipse 106
60. Huyghens’ eyepiece 110
61. Diagram explaining the achromaticity of the Huyghenian 111 eyepiece
62. Ramsden’s eyepiece 112
63. Erecting or day eyepiece 113
64. Images of planet produced by short and long focus lenses, &c. 123
65. Showing in an exaggerated form how the edge of the speculum 128 is worn down by polishing
65*. Section of Lord Rosse’s polishing machine 131
66. Mr. Lassell’s polishing machine 132
67. Simple telescope tube, showing arrangement of object-glass 140 and eyepiece
68. Appearance of diffraction rings round a star when the 141 object-glass is properly adjusted
69. Appearance of same object when object-glass is out of 141 adjustment
70. Optical part of a Newtonian reflector of ten inches aperture 143
71. Optical part of a Melbourne reflector 143
72. Mr. Browning’s method of supporting small specula 144
73. Support of the mirror when vertical 146
74. Division of the speculum into equal areas 147
75. Primary, secondary, and tertiary systems of levers shown 148 separately
76. Complete system consolidated into three screws 148
77. Support of diagonal plane mirror (Front view) 150
78. Support of diagonal plane mirror (Side view) 150
79. A portion of the constellation Gemini seen with the naked eye 154
80. The same region, as seen through a large telescope 155
81. Orion and the neighbouring constellations 156
82. Nebula of Orion 157
83. Saturn and his moons 160
84. Details of the ring of Saturn 161
85. Ancient clock escapement 177
86. The crown wheel 178
87. The clock train 180
88. Winding arrangements 181
89. The cycloidal pendulum 185
90. Graham’s, Harrison’s, and Greenwich pendulums 188
91. Greenwich clock: arrangement for compensation for barometric 194 pressure
92. The anchor escapement 197
93. Graham’s dead beat 199
94. Gravity escapement (Mudge) 200
95. Gravity escapement (Bloxam) 202
96. Greenwich clock escapement 204
97. Compensating balance 207
98. Detached lever escapement 208
99. Chronometer escapement 209
100. The fusee 209
101. Diggs’ diagonal scale 213
102. The vernier 214
103. System of wires in a transit eyepiece 220
104. Wire micrometer 221
105. Images of Jupiter 224
106. Object-glass cut into two parts 225
107. The parts separated, and giving two images of any object 225
108. Double images seen through Iceland spar 227
109. Diagram showing the ordinary and extraordinary rays in a 227 crystal of Iceland spar
110. Crystals of Iceland spar 228
111. Double image micrometer 229
112. Tycho Brahe’s mural quadrant 235
113. Transit instrument (Transit of Venus Expedition) 236
114. Transit instrument in a fixed observatory 237
115. Diagram explaining third adjustment 239
116. The mural circle 241
117. Transit circle, showing the addition of circles to the 242 transit instrument
118. Perspective view of Greenwich transit circle 243
119. Plan of the Greenwich transit circle 245
120. Cambridge (U.S.) meridian circle 248
121. Diagram illustrating how the pole is found 249
122. Diagram illustrating the different lengths of solar and 255 sidereal day
123. System of wires in transit eyepiece 257
124. The Greenwich chronograph. (General view) 261
125. Details of the travelling carriage which carries the magnets 262 and prickers. (Side view and view from above)
126. Showing how on the passage of a current round the soft iron 263 the pricker is made to make a mark on the spiral line on the cylinder
127. Side view of the carriage carrying the magnets and the 263 pointer that draws the spiral
128. Wheel of the sidereal clock, and arrangement for making 266 contact at each second
129. Arrangement for correcting mean solar time clock at Greenwich 268
130. The chronopher 276
131. Reflex zenith tube 286
132. Theodolite 288
133. Portable alt-azimuth 289
134. The 40-feet at Slough 294
135. Lord Rosse’s 6-feet 295
136. Refractor mounted on alt-azimuth tripod for ordinary 296 star-gazing
137. Simple equatorial mounting 298
138. Cooke’s form for refractors 300
139. Mr. Grubb’s form applied to a Cassegrain reflector 301
140. Grubb’s form for Newtonians 303
141. Browning’s mounting for Newtonians 304
142. The Washington great equatorial 309
143. General view of the Melbourne reflector 312
144. The mounting of the Melbourne telescope 313
145. Great silver-on-glass reflector at the Paris observatory 316
146. Clock governor 319
147. Bond’s spring governor 320
148. Foucault’s governor 323
149. Illuminating lamp for equatorial 325
150. Cooke’s illuminating lamp 326
151. Dome 338
152. Drum 338
153. New Cincinnati observatory—(Font elevation) 338
154. Cambridge (U.S.) equatorial 339
155. Section of main building—United States naval observatory 341
156. Foucault’s siderostat 344
157. The siderostat at Lord Lindsay’s observatory 348
158. Position circle 353
159. How the length of a shadow thrown by a lunar hill is measured 354
160. The determination of the angle of position of the axis of 358 Saturn’s ring
161. Measurement of the angle of position of the axis of a figure 359 of a comet
162. Double star measurement 360
163. Ring micrometer 368
164. Thermopile and galvanometer 374
165. Rumford’s photometer 378
166. Bouguer’s photometer 379
167. Kepler’s diagram 387
168. Newton’s experiment, showing the different refrangibilities 388 of colours
169. First observation of the lines in the solar spectrum 391
170. Solar spectrum 392
171. Student’s spectroscope 393
172. Section of spectroscope 394
173. Spectroscope with four prisms 396
174. Automatic spectroscope (Grubb’s form) 397
175. Automatic spectroscope (Browning’s form) 397
176. Last prism of train for returning the rays 398
177. Spectroscope with returning beam 399
178. Direct-vision prism 399
179. Electric lamp 404
180. Electric lamp arranged for throwing a spectrum on a screen 405
181. Comparison of the line spectra of iron, calcium, and 406 aluminium, with common impurities
182. Coloured flame of salts in the flame of a Bunsen’s burner 408
183. Spectroscope arranged for showing absorption 409
184. Geissler’s tube 413
185. Spectrum of sun-spot 415
186. Diagram explaining long and short lines 416
187. Comparison of the absorption spectrum of the sun with the 418 radiation spectra of iron and calcium, with common impurities
188. Comparison prism 423
189. Comparison prism 423
190. Foucault’s heliostat 424
191. Object-glass prism 426
192. The eyepiece end of the Newall refractor 427
193. Solar telespectroscope (Browning’s form) 428
194. Solar telespectroscope (Grubb’s form) 428
195. Side view of spectroscope 429
196. Plan of spectroscope 429
197. Cambridge star spectroscope elevation 430
198. Cambridge spectroscope plan 430
199. Direct-vision star spectroscope (Secchi) 431
200. Types of stellar spectra 433
201. Part of solar spectrum near F 436
202. Distortions of F line on sun 438
203. Displacement of F line on edge of sun 439
204. Diagram showing the path of the ordinary and extraordinary 445 ray in crystals of Iceland spar
205. Appearance of the spots of light on the screen shown in the 446 preceding figure, allowing the ordinary ray to pass and rotating the second crystal
206. Appearance of spots of light on screen on rotating the second 447 crystal, when the extraordinary ray is allowed to pass through the first screen
207. Instrument for showing polarization by reflection 448
208. Section of plate-holder 456
209. Enlarging camera 458
210. Instantaneous shutter 460
211. Photoheliograph as erected in a temporary observatory for 461 photographing the transit of Venus in 1874
212. Copy of photograph taken during the eclipse of 1869 474
213. Part of Beer and Mädler’s map of the moon 476
214. The same region copied from a photograph by De La Rue 477
215. Comparison between Kirchhoff’s map and Rutherfurd’s 480 photograph
216. Arrangement for photographically determining the coincidence 481 of solar and metallic lines
217. Telespectroscope with camera for obtaining photographs of the 482 solar prominences