President’s Address. 17 
and a complete set of magnetic instruments, both for abso- 
lute and differential determinations. 
The work of the Observatory, besides the ordinary rou- 
tine of observations for some instrumental errors, meteorology 
and magnetism, has consisted principally of a revision of 
star catalogues, with the immediate view of completing the 
Williamstown Star Catalogue now in the press. This 
volume, which will shortly be published, will contain the 
results of all the work done of late years at the Williamstown 
Observatory in Melbourne, up to the date of its removal, and 
will contain a complete catalogue of the places, precessions, 
proper motions, &c., 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 Cape 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 
* “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"'5770, 
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 is more precisely 185,170 (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 0"'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 original 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.” 
B 
