AND A SELECTION EEOM THE OBSEEVATIONS MADE WITH THEM. 701 
into one slide, so that there are always two eyepieces, a high and a low power, which 
may be employed successively simply by moving the slide. The slide is counterpoised, 
and the eyepieces fit in "without screws. The telescope is perfectly steady even in a 
high "wind, and we have had occasionally very fine definition during a strong gale. 
From the experience we have now had, I think I may safely say that, where objects 
are to be obsem'ed only at short distances from the meridian, this plan of mounting is 
convenient and efiective, and I do not see room for any material improvement. Where 
observations are carried on systematically, I do not think there is very much dis- 
advantage in the limited movement in right ascension. Objects are best seen near the 
meridian, and no object can be thoroughly examined in any other position. There is, 
indeed, a small portion of the heavens which can scarcely be observed in the perfect 
absence of twilight, and an object there situated would probably be better seen, even at 
some distance from the meridian, when it was perfectly dark ; but that seems to be of 
little moment. The really important disadvantage of the limited equatorial movement 
seems to me to be this, that, where fine nights are extremely rare, with an instrument 
so limited it is impossible to turn them to the best account. 
It now only remains to answer in the best way I can the questions — 
First, What magnifying power can be usefully employed with a speculum of 6 -feet 
aperture 1 I perceive, in looking through the observations, that the single-lens eye- 
piece, 5 -inch focus, being a power of about 1300, is often mentioned as giving better 
\ision than lower powers. That, I presume, may be considered the highest power it 
has been found advantageous to employ in general observations upon the nebulse. 
With the speculum of 3-feet aperture I have occasionally employed powers exceeding 
2000 in bringing out minute stars ; and the speculum of 6 -feet aperture has sometimes 
been in sufficiently good order to admit of equal or perhaps higher powers ; but in our 
climate the opportunities of employing such powers are rare, and of short duration. 
Secondly, it has been asked, Could a telescope be made of larger dimensions, and 
would it be of seindce 1 I feel little doubt that both questions should be answered in 
the affirmative. A speculum of larger aperture would, probably, on favourable nights 
bring out faint details of interest in the nebulae, and add to the number of known double 
and multiple nebulae. Something, however, will perhaps be accomplished in that direc- 
tion in our future observations, by employing silver for the second reflexion ; but if ever 
telescopes of equal power are erected in climates more favourable than this, perhaps 
more "will be effected than would be possible here by pushing increase of aperture to 
the largest practicable limits. 
In making a selection from observations so numerous, there has been considerable 
difficulty. It was not always easy to decide how much it would be practicable to omit 
without the danger of conveying an erroneous impression — without, on the one hand, 
perhaps unduly weakening the evidence of the fact recorded, or, on the other, unduly 
strengthening it. For instance : if, in the observations of a particular object, we find it 
recorded on six different nights that a minute star was seen involved, and that on six 
