for the year 1864. lxxxi 



Observatory in Melbourne, up to the date of its removal, and 

 will contain a complete catalogue of the places, precessions, 

 proper motions, fee., of 550 stars, the results of 9,000 complete 

 observations. It will also contain the "Series of Mars 

 Observations," taken in connection with Greenwich, Pulkowa, 

 and Gape of Good Hope, for the determination of the sun's 

 mean distance. 



This series has made our Colonial Observatory already 

 famous at home, and is very favourably referred to in the 

 Quarterly Review of Science, as in the note at foot of the 

 page* The Magnetic Survey of the Colony was completed 

 in the month of January of the present year. The last work 

 was the survey of Gipps Land, in which part of the colony 



* " To Encke we owe the best discussion of the observations of the transit 

 of Venus in 1769 : he determined the value of the sun's parallax to be 8"-5776, 

 from which we infer the earth's mean distance from the sun to be 95,283,115 

 miles. Now the time occupied by a ray of light reaching the earth from the 

 sun is known very exactly to be 8 min. 13 sec, from which a velocity of about 

 192,000 miles per second is deducible. Foucault, of Paris, however, by the 

 optical contrivance of a ' turning mirror,' due to Professor Wheatstone, has 

 concluded that this value is too great, that it ismore precisely 1 85,1 70 (English) 

 miles. Assuming that Foucault is right, and all his predecessors wrong, it 

 follows that the solar parallax must be 8"-86. Two most singular coincidences 

 must here be disposed of. (1.) The ' theoretical' value assigned by Le Verrier, 

 irrespective of all instrumental measurements, and purely on physical 

 grounds, is 8"-95 ; and (2.) the discussion, by Stone, of Greenwich, of the obser- 

 vations of Mars (adverted to above in Mr. Hind's 6th point) taken by Ellery 

 at Williamstown, Victoria, N.S. W., give a value of 8"-93, with a probable error 

 of only //, 03. Combining the foregoing, we find that three different observers, 

 working in three most diverse ways, have all arrived at the same general 

 result, and more than this, at actual valuations, the extremes of which differ 

 only by the minute amount of 0"*09. It is impossible for us to withstand the 

 conclusion that our estimations so long adhered to must sooner or later be 

 materially ' reconstructed,' and, as a consequence, that those portions of our 

 treatises involving this distance must be unceremoniously pulled to pieces 

 and built up again. An origiual calculation of the mean distance of the 

 earth from the sun, amended according to Stone and Ellery 's value of the 

 parallax, makes it 91,512,649 miles." 



F 



