7 
have of extending our knowledge, seems to be l)y carefully sketchintr 
and measuring every object sufficiently within reach of our instrm 
ments, to make details discernible. It is highly probable that the 
objects we see are presented to us in every variety of position, that 
they often differ in form merely because we see them in a different 
aspect, and that if all were similarly placed as to the line of sight, a 
few normal forms would represent the whole. If this is the case, 
had we a sufficient number of accurate sketches, it is probable that 
out of the apparent confusion we should succeed in extracting the 
normal forms. It is also probable that in the nebular systems 
motion exists. If we see a system with a distinct spiral arrangement, 
all analogy leads us to conclude that there has been motion, and 
that if there has been motion that it still continues. The apparent 
motion is probably very slow, owing to the immense distance of the 
nebulse ; still there are double stars known to be physically double 
from their motions, which are probably as distant as some of the 
nebulse. In certain nebulse stars are so peculiarly situated that we 
can scarcely doubt their connection with the nebular system in 
which we see them, and some of these stars are as bright as some 
of the stars known to be physically double ; as bright even as some 
of the stars which the latest Pulkowa observations have shown to 
have sensible parallax, and whose distance therefore is approximately 
knowm. We have therefore some vague idea, resting on probable 
evidence, even of the distance of the nearest nebulse. It seems there- 
fore not unreasonable to expect that measurements perseveringly 
carried on will detect motion, and that a fulcrum will thus 'be 
obtained, by which the pow’ers of analysis may be brought to bear 
upon the laws which govern these mysterious systems. 
In the northern catalogue of Nebulse, and the same observation 
no doubt applies to the southern also, there are vast numbers much 
too faint to be sketched, or measured, with any prospect of advan- 
tage ; the most powerful instruments we possess, showung in them 
nothing of an organized structure, but merely a confused mass of 
nebulosity of varying brightness. The number of nebulae in the 
northern hemisphere, in which details are w'ell brought out, 
is not very large, and even in these, a great proportion of the 
measurements are necessarily rough, and wanting in that precision 
by which the motion of certain double stars was so soon detected. 
It is evident therefore that to obtain a true knowledge of the forms 
of the nebular systems, our sketches must be as numerous as possi- 
ble ; and to obtain evidence of motion with rough measures, our 
measures should be very numerous also ; but the northern hemi- 
sphere pesents but a very limited list of suitable objects, therefore 
it is desirable to take in the southern hemisphere also. 
I have thus, I believe, in part at least, explained the views of 
those who felt anxious that the southern hemisphere should be exa- 
mined with a telescope of great power : the first attempt to give 
practipl elfect to their wishes was at the meeting of the British 
Association held at Birmingham in 1849. 
The President of the Association was on that occasion directed to 
