4go Sir W. Herschei/s astronomical observations 
to contain all the stars that in the clearest nights are visible 
to the eye of an observer. 
I. Of the distance of globular and other clusters of stars. 
In observations which are made for ascertaining the dis- 
tance of a cluster of stars, it is necessary that the gaging 
power should be marked, which will just make some of the 
stars belonging to it visible in the telescope that is used for 
this purpose. If the cluster is of a globular form, but is not 
insulated, the stars that belong to it may be easily distin- 
guished from those which may happen to be scattered about, 
or upon it. In clusters of a different construction, the com- 
pression, or the apparent size of the stars, must direct the 
observer. 
It is to be remarked, that neither the brightness, nor the 
diameter of the clusters of which the distance is to be ascer- 
tained, are to be considered : some of them are bright enough 
to be perceived by the eye ; others are visible in the finder of 
the telescope, and many of them can only be seen in the 
telescope itself. These are circumstances that have no in- 
fluence on the exactness of the result of the gaging power ; 
but as they regard our knowledge of the construction of these 
magnificent sidereal systems, an abridged account of them is 
given, with the observations by which their profundity in space 
is ascertained ; and in the arrangement of these observations, 
I have followed the order of the space-penetrating power of 
the instruments by which they were made. 
In recording the examination of celestial objects, I have 
often applied to them the expressions resolvable, or easily 
resolvable, when, from their appearance, I could not decide 
