xxvi LIST OF ILLUSTRATIONS ON WOOD. 



FIG. PAGE 



189. Path of luminous rays in Galileo's telescope $;..*.. 251 



190. Achromatic lenses : Gauss' object-glass ; Herschel's object-glass ... . 253 



191. Opera-glass with achromatic object-glass and eye-piece . . . . . . 254 



192. Double or binocular opera-glass . Y . . 254 



193. Path of the luminous rays in the inverting telescope 255 



194. Inverting telescope ; section or inner view . 256 



195. Astronomical refractor with finder mounted on ordinary stand . . . 256 



196. Theodolite level 257 



197. Theodolite (another form) 258 



198. Perspective view of the transit circle at Greenwich 259 



199. A portion of the constellation Gemini, seen with the naked eye . . . 260 



200. The same portion of the heavens seen with a telescope of 27 centimetres 



aperture 261 



201. Path of the luminous rays in the erecting telescope ....... 262 



202. Principle and arrangement of Sir W. Herschel's (front view) telescope 264 



203. Sir W. Herschel's large telescope (front view) at the Slough Observa- 



tory 267 



204. Principle and arrangement of Gregory's telescope 269 



205. Gregory's telescope 270 



206. Principle and arrangement of Newton's telescope 273 



207. Leon Foucault's telescope with silver mirror (Newtonian system) . . 274 



208. Difference between monocular and binocular vision . 280 



209. Wheats tone's reflecting stereoscope 281 



210. Stereoscopic proofs. Facsimile of a photograph representing one of 



the rooms in the Louvre 282 



211. Refracting stereoscope : section 284 



212. Refracting stereoscope : external view 284 



213. Helmholtz's stereoscope 285 



214. The pseudoscope 286 



215. Direct and inverse stereoscopic vision : relief and hollow 287 



216. Pseudoscopic vision : medallion of Moliere 287 



217. Mercury box for developing daguerreotypes 293 



218. Photographic camera 304 



219. Country photographic apparatus, bellows shape 305 



220. Simple object-glass 306 



221. Complex object-glass with adjusting lens 306 



222. Microscopic photograph. Facsimile of a despatch sent to Paris during 



the siege . 311 



223. Enlarging and reading the microscopic despatches during the siege of 



Paris 312 



224. Facsimile of a heliographic engraving 316 



225. Photographic microscope . . ' . . . . 325 



226. Minute disc : Arachnoidiscus. Facsimile of a microscopic photograph 326 



227. A savage making fire ...,..- 334 



228. A Spanish brasero 335 



229. A Roman foculus ....... 335 



230. Warming among the ancients. Grecian tripods . . 336 



231. Draught in an ordinary fireplace 338 



