702 EAEL OE EOSSE ON THE CONSTETJCTION OE SPECULA OE 6-EEET APEETUEE, 
other nights it was not seen at all, the twelve observations extending over a series of 
years, two cases might arise requiring very different treatment. First, if the nights when 
the star was visible were irregularly interspersed between the nights when the star was 
invisible, and we saw enough in the state of the atmosphere or speculum to account for 
the occasional invisibility of the star, it would probably be quite sufficient to enter one 
good observation when the star was distinctly seen. Suppose, however, that the nights 
when the star was seen were all included in the observations of the first three years, 
but that the nights when the star was not seen were in the observations of the last three 
years, then it would be necessary to enter all the observations, so that each person 
might he enabled to form his own opinion as to the cause of the discrepancy. 838 H., 
fig. 11, in the ‘Transactions’ for 1850, is a remarkable instance of this: from 1850 to 
1858 the small star was not seen. 
The details of faint nebulae with curved or spiral branches have usually been made 
out by degrees, not only on successive nights, but often in successive years. In such 
cases we have not usually thought it necessary to give the early observations, or the 
observations on unfavourable nights, but merely a few good observations embodjdng the 
whole amount of information we had been enabled to obtain. 
New nebulae have not been looked for, our object being to scrutinize the more pro- 
mising of the old ones ; but new nebulae have often been found in their immediate 
neighbourhood, and their places have usually been entered roughly in the obser'ring- 
book, and a slight diagram made in the margin, so as to ensure their being easily found 
again: in such cases we have, to save space and diagrams, merely written “novae near,” 
and have only entered observations when the micrometer was employed. We have also, 
for the same reason, omitted many diagrams of known objects, where the positions and 
distances were merely estimated. 
In the case of each object, we say “ observed so many times that means that we have 
recorded observations of it on so many different nights: it may have been seen ffe- 
quently on other occasions. 
Where an object has been marked “ observed several times,” and nothing more, the 
inference is that with an instrument such as ours is, and in our climate, it would be 
waste of time to examine it further in the hope of making out details of interest. 
It will be observed that the cases are very numerous where stars have been seen on 
the edges of nebulae: we have taken care to enter each case, often, however, on the 
authority of a single good observation, as before explained. 
The words “ mottled ” and “ patchy ” mean the same thing. "YNTiere the nebula is of 
that character, it is worth examining under favourable circumstances. The faint sphals 
have often been first seen as “ mottled.” 
The word “ finder ” means the eyepiece with a large field. The telescope has no 
finder in the common acceptation of the word. 
The letter “r” has been occasionally added to the description, and always in the same 
sense as that in which Heeschel employed it : I do not, however, attach much import- 
