Observations of Nebule and Clusters of Stars. 3 
only since 1871 that by noting down the time at each measure we have had the 
data for applying a correction. 
To many, however, of the measures of earlier years, an approximate correction, 
based on an assumption as to the probable interval which had elapsed since 
the object was on the meridian, has been applied. Those earlier measures to which 
no correction has been applied 2 are only given in round numbers without fractions 
of a degree. 
Up to the year 1871 the zero of position was determined for each set of measures 
by means of a spirit-level attached to the micrometer-head, but subsequently by 
turning the micrometer in the course of each night, so as to make stars run along 
the edge of one of the bars. A “feather” firmly screwed on to the adaptor in the 
year 1873 has now made the zero return almost exactly to the same value night 
after night. 
The exact value of the micrometer screw employed in the reductions is— 
One turn — 657113. 
It was found by measuring the distances between stars in the Pleiades, as the 
construction of the instrument does not permit of its being brought near the 
North Pole. 
The number of single measures combined in a result is in each case indicated by 
a figure in brackets, e.g. Pos. 268°.9 (2), Dis. 74.8 (3), implies that two measures 
of position-angle and three of distance were made. Where no number is given, a 
single measure only was taken. 
To facilitate the preparation of the observations for publication they have been 
divided into three Parts. Part I. embraces the first eight hours (0" to 8") of Right 
Ascension ; Part II. embraces the next six hours (8" to 14") ; but for these regions 
of the heavens each part is complete in itself. In a Third Part it is proposed to 
continue the series through the remaining ten hours of Right Ascension. 
It has been found convenient, where two or more nebule are so near as to be in 
the field together or nearly so, to place them in one group, even though numbered 
separately in the catalogues. Some difficulty has now and then arisen in regions 
rich in nebulee in identifying the object observed witha catalogued nebula, but it is 
believed that by comparing the observations inter se and with those of the two 
Herschels, D’Arrest, Schultz, and others, and by re-observation where necessary, 
very few cases of uncertain identity remain, and these are noted. All the remarks 
in square brackets were added by the transcriber while arranging the observations 
for publication ; in no case do they form a part of the original notes. 
Where measures from a neighbouring star, which has subsequently been identified 
with one in a catalogue, or from a neighbouring nebula whose place is more accura- 
tely known enable us to do so, the calculated place of a “Nova” or of a nebula, 
whose position is less accurately given in the general catalogue, is inserted among 
these notes in square brackets. For obvious reasons, such as the yielding of the 
B 2 
