4 
SIE J. F. W. HEESCHEL’S CATALOGUE 
antecedent place of the object will be exactly compensated by the further change of 
place in the same direction in the subsequent fifty. Two cases of excessive proximity to 
the poles, northern and southern, viz. those of the nebulae Nos. 2043 and 1652 of the 
present Catalogue, are excepted, the precessions changing so rapidly, and with so much 
deviation from uniformity, that a rigorous computation, at least in R.A., will always be 
necessary. In the case of No. 2043, the effect of precession in the thirty years from 
1830 to 1860 has been to change the R.A. from 2 h 32 m to 10 h 8 m . 
This computation was completed, and a fair copy of the resulting places, arranged de 
novo in their order of R.A. for 1860, forwarded to me on the 6th of February last (1863). 
The nomenclature of the objects having in the interim been settled satisfactorily by 
myself, and a description of each nebula, from a careful comparison of all the descriptions 
given, prepared, it remained only to fill in the columns left blank for these and the other 
necessary particulars, and to complete the Catalogue by the insertion in their proper 
places of the places and descriptions of all such other nebulae, non-observed by either my 
Father or myself, similarly reduced, of which I could gather any accounts. These will be 
found enumerated further on in the “ Explanation and arrangement of the Catalogue.” 
On the 23rd of February last, while engaged in this work, I received, by the kindness 
of the Astronomer Royal, a copy of the important work of M. Auwers before alluded 
to, entitled “ William Herschel’s Verzeichnissen von Nebelflecken und Sternhaufen, 
bearbeitet von Arthur Auwers. Konigsberg, 1862,” of whose existence this was my first 
notice. It contains a complete and most elaborate reduction to 1830, from the observed 
differences in R.A. and P.D. with known stars, recorded in the Philosophical Transac- 
tions, of all the nebulae and clusters in my Father’s three Catalogues ; together with a 
separate catalogue of all those collected by Messier from his own observations, or those of 
Mechain and others (101 in number), similarly reduced ; another of Lacaille’s southern 
nebulae, and one of 50 “ new nebulae,” comprising nearly all those observed by other astro- 
nomers (Lord Rosse excepted) in this hemisphere — all brought up to the same epoch. 
It may be readily supposed that I lost no time in comparing my own previous work 
with this of M. Auwers ; the places of which having been obtained by the aid of far 
better and more dependable catalogues of stars, to give the true positions of the zero- 
points or determining stars in the differential observations, as well as of more exact pre- 
cessions, and doubtless, a much more systematic process of treatment, would be entitled, 
observation for observation , to be considered as representing the original sweeps more 
faithfully than could be expected from my own preparatory catalogue. On the other 
hand, however, the Zone Catalogue from which that was derived possessed the advantage 
of having been deduced, not from a single difference of R.A. and P.D. between each 
nebula and a single determining star, but from all the observations of each nebula ; 
often in many different sweeps, and in the same sweep often from more than one star ; 
thus eliminating, no doubt, a great deal of casual error. In that catalogue, too, as in 
my own catalogues of 1833 and that of the southern nebulae, the individual results of 
each observation, or, to speak more exactly, of each differential comparison, is separately 
