10 
SIR J. E. W. HEESCHEL’S CATALOGUE 
municated to the Royal Society ; the other 8 are printed in the form of an Appendix to my 
Cape Catalogue, in p. 128 of the “ Results of Observations,” &c. A similar and separate 
Register in sheets has been kept for my Father’s observations of Messier’s nebulae, and 
these have in like manner been collated with my own observations of the same objects 
in framing the ultimate, or, as it may be termed, the average description of each. 
In making out these descriptions, it was found to a certain degree practicable, in the 
particulars of brightness, size, and extension, to make a kind of arithmetical approxima- 
tion to a mean conclusion, by arranging the degrees of brightness, &c. in a progressive 
upward scale from 1 to 10, and taking a mean of these numbers in each case, as indi- 
cating the designating words to be finally adopted. Thus, taking the extreme degree of 
faintness when a nebula was declared to be “ excessively faint,” or “ barely visible,” or 
“ hardly more than suspected ” for 1, and “ extremely ” or “ excessively bright ” for 10, 
the intermediate degrees, such as very faint , faint , considerably faint , pretty faint , 
pretty bright , considerably bright , Bright , very bright , were denoted by the intermediate 
numbers 2, 3, 4, 5, 6, 7, 8, 9 ; and similarly for the scale of sizes, exchanging the words 
Small and Large for Faint and Bright. In the case of extension, the scale 1 to 10 was 
supposed arranged in the order, Bownd, very little extended , elliptic or oval , considerably 
extended , pretty much extended , much extended , very much extended , extremely extended , 
or a long ray. It is obvious that the qualifying words, such as “ pretty” and “ consider- 
ably,” admit of a good deal of latitude of interpretation, and that, in reference to bright- 
ness or faintness, greatness or smallness, their meaning is rather relative than absolute ; 
and especially, that as between bright or faint, and “ considerably bright” or “consider- 
ably faint,” for instance, there is so little real distinction of an absolute kind, that it is 
impossible to say which is to be accepted as indicating the superior degree. In the case 
of extension there is the same indistinctness as to precedence between the qualifying 
phrases “ considerably” and “ pretty much.” Nicety, however, in this respect would be 
misplaced, when it is considered that when several descriptions of the same nebula, 
observed at different times, come to be compared, they can hardly ever be reconciled 
except by allowing to each qualification a latitude of meaning extending over several 
degrees of our arbitrary scale. In many instances, indeed, the discordance, or rather 
contradiction is so great, as to authorize a strong suspicion of variability in the object 
itself. In a few cases where, from the low altitude of the object in England, coupled with 
corresponding discordances of description, it was evident that it must have been seen to 
much greater advantage from the Cape station (as, for example, in that of h. 3375 = 11. 
III. 754), additional weight has been attributed to the Cape observations. 
In the descriptions, I have found it absolutely necessary to abstain from any specifi- 
cation of the estimated sizes of nebulae or clusters in angular measure. In comparing 
estimations of this kind I find the discordance so great, and (to speak only of my own 
practice) so little evidence of adherence to any definite standard of estimation, that 
nothing but confusion would have arisen from introducing such estimates. Never- 
theless, as in the use of such a catalogue as the present some guide is necessary for the 
