A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE 



" To the solid grouna 

 Of Nature trusts the mind which builds for aye." — WORDSWORTH 



THURSDAY, NOVEMBER i, 1877 



TI/£ SUN'S DISTANCE 



A MO ST interesting state paper has just been issued ; we 

 refer to the Report by the Astronomer- Royal on the 

 Telescopic Observations of the Transit of Venus of 1874, 

 made by the Expeditions sent out by the British Govern- 

 ment and the results deduced from them. The Astro- 

 nomer-Royal suggests that another report may be called 

 for when the photographs of the transit have been com- 

 pletely measured and worked out, if possible in combina- 

 tion with the results of similar observations made in the 

 expeditions organised by other governments. 



It will be seen from the present Report that the plan of 

 operations actually pursued has been very nearly that 

 proposed by the Astronomer- Royal in his communication 

 to the Royal Astronomical Society on December 11, 1868, 

 when for the third time directing attention to the arrange- 

 ments which it would be necessary to make for the 

 efficient observation of the transits of 1874 and 1882. 

 The method of absolute longitudes was to be applied for 

 observations both of ingress and egress ; it being therefore 

 essential that the longitudes of the observing-stations 

 should be determined with precision ; and the longitudes 

 recommended to be fixed by Great Britain were Alex- 

 andria, stations in New Zealand and in the Sandwich 

 Islands, Kerguelen's Land, and Mauritius or the two 

 islands of Rodriguez and Bourbon. 



The stations eventually selected for observations by the 

 British expedition were fixed upon "entirely by considera- 

 tion of the influence which their positions would have in 

 determining with accuracy the necessary alteration of 

 parallax." They were : Egypt, the Sandwich Islands, the 

 Island of Rodriguez, New Zealand, and Kerguelen's Land. 

 It was intended to adopt in each of these districts one fun- 

 damental station, the longitude of which was to be inde- 

 pendently determined, for conversion of local times into 

 Greenwich times, and subordinate to thii primary station, 

 other stations were proposed to be selected at such 

 distances that advantage might be taken of different 

 states of weather that might possibly prevail. 



In Egypt his Highness the Khedive rendered every 

 Vol. xvii.— No. 418 



possible assistance, tents being supplied with military 

 guards for the protection of the observers and their in- 

 struments, and telegraph wires erected. The Astronomer- 

 Royal acknowledges the obligations of the expedition to 

 the liberality of the Eastern Telegraph Company, in 

 affording the means of determining with extreme ac- 

 curacy and great facility the longitude of the principal 

 station Mokattam. Greenwich was easily connected with 

 Forth Curno, in Cornwall, whence there is an unin- 

 terrupted line to Alexandria, the longest submarine line 

 in the world ; Alexandria was connected with Mokattam 

 by aid of the special line constructed by the Khedive 

 from Cairo to the station. It is further stated that time- 

 communication was also made from Mokattam through 

 Cairo to Thebes, and to Suez by the ordinary telegraph, 

 Thebes and Suez being the other Egyptian stations where 

 the transit was observed. 



In the Sandwich Islands much assistance was received 

 from King Kalakaua and members of the reigning family. 

 The principal station was at Honolulu, the longitude of 

 which was determined partly by meridian- transits of the 

 moon and partly by transits of the moon observed with 

 the Altazimuth instrument. Waimea, in the island 

 Kauai, where observers were also placed, was connected 

 with Honolulu by means of chronometers carried in 

 H M.S. Teredos. At the Island of Rodriguez the longi- 

 tudes were determined in the same manner as for the 

 Sandwich Islands stations, for three positions, viz.. Point 

 Venus, the Hermitage, and Point Coton ; and com- 

 munication was further made with the Mauritius and with 

 Lord Lindsay's expedition with the aid of H.M S 

 Shear-water, the preliminary results being stated by Sir 

 George Airy to agree closely with those given by the 

 lunar observations. At Kerguelen's Land, again, the 

 operations were similar ; Supply Bay and Thumb Peak 

 being the stations chosen. 



In New Zealand unfavourable weather much interfered 

 with the observations, and Sir George Airy had at first 

 been led to suppose that all useful observation had been 

 lost ; it subsequently appeared, however, that this was 

 not the case, one phase of the transit being well seen at 

 Burnham, the longitude of which was fixed by meridian 

 transits of the moon. 



The Report is divided into three sections or tables. 



