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