12 PRESIDENTS ADDRESS. 
considerable detail. But I have not there made adequate reference to 
the labours of Dr. Gould and Dr. Thome at Cordoba. To their labours, 
combined with the work done under Stone at the Cape, we owe the fact 
that for the epoch 1875 the meridian sidereal astronomy of the southern 
hemisphere is nearly as well provided for as that of the northern. 
The point I wish to make is that the facts of exact sidereal astronomy in 
the southern hemisphere may be regarded as dating nearly a hundred 
years behind those of the northern hemisphere. 
The Constitution of the Universe. 
It was not until 1718, when Edmund Halley, afterwards Astronomer 
Royal of England, read a paper before the Royal Society,! entitled 
‘ Considerations on the Change of the Latitudes of Some of the Principal 
Fixt Stars,’ that any definite facts were known about the constitution of 
the universe. In that paper Halley, who had been investigating the 
precession of the equinoxes, says: ‘ But while I was upon this enquiry 
I was surprized to find the Latitudes of three of the principal Stars in 
heaven directly to contradict the supposed greater obliquity of the 
Keliptick, which seems confirmed by the Latitudes of most of the rest.’ 
This is the first mention in history of an observed change in the 
relative position of the so-called fixed stars—the first recognition of what 
we now call ‘ proper motion.’ 
Tobias Mayer, in 1760, seems to have been the first to recognise that 
if our Sun, like other stars, has motion in space, that motion must produce 
apparent motion amongst the surrounding stars ; for in a paper to the 
Gottingen Academy of Sciences he writes : ‘Tf the Sun, and with it the 
planets and the Earth which we inhabit, tended to move directly towards 
some point in the heavens, all the stars scattered in that region would 
seem to gradually move apart from each other, whilst those in the 
opposite quarter would mutually approach each other. In the same 
manner one who walks in the forest sees the trees which are before him 
separate, and those that he leaves behind approach each other.’ No 
statement of the matter could be more clear ; but Mayer, with the meagre 
data at his disposal, came to the conclusion that ‘the motions of the 
stars are not governed by the above or any other common law, but belong 
to the stars themselves.’ 
Sir William Herschel, in 1783, made the first attempt to apply, with 
any measure of success, Mayer’s principle to a determination of the 
direction and amount of the solar motion in space. He derived, as well 
as he could from existing data, the proper motions of fourteen stars, and 
arrived by estimation at the conclusion that the Sun’s motion in space is 
nearly in the direction of the star \ Herculis, and that 80 per cent. of the 
apparent motions of the fourteen stars in question could be assigned to 
this common origin. 
1 Phil. Trans., 1718, p. 788. ? Lbid., 1783, p. 247. 
