LORD OXMANTOWN ON THE REFLECTING TELESCOPE. 
525 
In selecting the materials for this communication from a vast mass of experi- 
ments, I have endeavoured to collect together such results as were most likely to be 
useful, and to work the whole into a shape as practical as possible, compressing it at 
the same time into the smallest compass : there are many minor matters of detail, 
which, therefore, I have unavoidably omitted; some of them possibly might be valuable 
to men of science, who maybe disposed to take up the subject practically with a view 
of proceeding further than I have done. I have, however, the less regret on this 
account, as, although the instrument and the laboratory where it was constructed 
are in the centre of Ireland, the facilities of communication are such, that those who 
may desire further information, can easily obtain it on the spot, and form their own 
estimate of the performance of the instrument. 
Since the commencement of last September, when the telescope was completed and 
in perfect working order, till Christmas, all opportunities which presented themselves 
for observing, not very many indeed, were taken advantage of. A considerable 
number of Sir John Herschel’s test objects were examined, and the performance of 
the instrument was quite satisfactory ; but as to double stars, perhaps the most stri- 
king contrast between its action and that of other instruments, was the extreme bril- 
liancy of the minute companions of large stars ; for instance, the companion of 
Polaris, with six hundred, was very like Polaris itself in a forty-four inch achromatic, 
with a two and three quarter object glass. The companions of Alpha Lyrse, and Rigel, 
were brilliant objects. As to the nebulae, though it was impossible not to feel per- 
suaded that a larger, and equally perfect instrument would have done much more, 
still there was enough, I think, to justify a confident expectation, that even the pre- 
sent instrument will add something to the very little that is known respecting these 
wonderful bodies. I think I might almost venture to say that the nebulae, 27 Mes- 
sier, the annular nebula in Lyra, and what is perhaps more curious, the edge of 
the great nebula in Andromeda, have shown very evident symptoms of resolvability; 
as also other nebulae less remarkable*. The appearance is that of a resolvable 
nebula in a telescope not quite powerful enough to resolve it completely. No such 
appearance, however, was observed till the power reached six hundred, and some- 
times it was more decisive with powers of eight hundred and one thousand. 
It is evident, therefore, that, except for the discovery of very faint nebulae, an object, 
perhaps, of but little interest, nothing would be effected by constructing a telescope 
of the greatest dimensions, unless it was at the same time proportionately perfect ; 
that a mere light grasper would do nothing. 
This instrument acts very powerfully on the lunar surface, and, as might be sup- 
posed, shows everywhere a variety of details not marked in the beautiful map of Beer 
* In describing the appearance of these bodies, I am anxious to guard myself from being supposed to con- 
sider it certain that they are actually resolvable, in the absence of that complete re-solution which leaves no 
room for error ; nothing but the concurring opinion of several observers could in any degree impart to an in- 
ference the character of an astronomical fact. 
