62 Royal Society. 



obtained, by which the powers of analysis may be brought to bear 

 upon the laws which govern these mysterious systems. 



In the northern catalogue of Nebulae, and the same observation 

 no doubt applies to the southern also, there are vast numbers much 

 too faint to be sketciied, or measured, witli any prospect of advan- 

 tage ; the most powerful instruments we possess, showing 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 well 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 soou 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 presents 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 

 practical effect 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 

 apply to Government to send a telescope of great power, in charge 

 of an experienced observer, to the southern hemisphere. That 

 application svas unsuccessful ; the Government, while they acknow- 

 ledged the importance of the proposedobject, declined to proceed, from 

 an apprehension of difficulties, through Avhich they did not then see 

 their way clearly. At a subsequent meeting of the British Association, 

 the matter was again discussed, and a Committee was appointed, to 

 take such measures as they considered best calclated to effect the 

 object. The Committee, in the first instance, laid the whole matter 

 before your Council, and the Council, approving of the suggestion, 

 appointed a Committee to consider the subject in detail. 



It was necessary before the Government could be applied to with 

 a reasonable prospect of success, that a specific plan should be in 

 readiness, complete in all its details : the size of the instrument, its 

 optical principle, its mounting, and its site. 



With the view of obtaining the best information, the Committee 

 consulted several eminent men, conversant with the management of 

 large instruments. The first question ]n-oposed was, whether the 

 instrument should be a refractor or reflector, and it was decided in 

 favour of the reflector — there was in fact no choice. In the present 

 state of knowledge, there was no probability that a good refractor 

 could be constructed of sufficient power. As to size, the Committee 

 were disposed to recommend a telescope of 4 feet aperture, and 

 35 feet focal length, to be mounted equatorially; not that an instru- 

 ment of that size was the best, a much larger no doubt would have 



