4,6o Sir W. Herschei/s astronomical observations 
is compensated by the advantage it has of showing all the 
angles of elevation, and the comparative lengths of the lines 
expressing the profundity of the clusters in their true mag- 
nitude, which an orthographic projection of their situation 
could not have done. 
IV. Of ambiguous celestial objects. 
When the nature or construction of a celestial object is 
called ambiguous, this expression may be looked upon as 
referring either to the eye of the observer, or to the telescope 
by which it has been examined. In the foregoing observa- 
tions we find that the nth, 13th, 15th, and 35th of the 
connoissance, when they are at a sufficient altitude for the 
purpose, may be seen by the eye ; but as, without artificial 
vision, they appear only under the semblance of very small, 
faint cloudy spots, we should not be able to decide whether 
they were of a nebulous or sidereal condition, if we were not 
informed by the telescope that they are brilliant clusters of 
stars ; the eye therefore sees them as ambiguous objects. 
If these objects are ambiguous when only viewed by the 
unassisted eye, there are others that will appear to be so, 
when they are seen through such small telescopes as are 
generally attached to large ones, and are called finders, 
because they point out objects that are not visible to the eye. 
With regard to these finders, I have occasionally used them 
of different sizes and constructions ; but from experience I 
can say, that a small one of a most simple composition, with 
a power of penetrating into space of about four times that of 
the eye, has generally been sufficient for all the purposes of 
a 7 or 10 feet telescope ; because these instruments may 
