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