roups sufficiently insulated and
condensed to come under the designation of 'clusters of
stars.'"--_Cape Observations_, p. 146.

In his _Outlines of Astronomy_, Sir John Herschel, after repeating this
description in other words, goes on to remark that--

"This combination of characters, rightly considered, is in a high
degree instructive, affording an insight into the probable
comparative distance of _stars_ and _nebulae_, and the real
brightness of individual stars as compared with one another. Taking
the apparent semidiameter of the nubecula major at three degrees,
and regarding its solid form as, roughly speaking, spherical, its
nearest and most remote parts differ in their distance from us by a
little more than a tenth part of our distance from its center. The
brightness of objects situated in its nearer portions, therefore,
cannot be _much_ exaggerated, nor that of its remoter _much_
enfeebled, by their difference of distance; yet within this
globular space, we have collected upwards of six hundred stars of
the seventh, eighth, ninth, and tenth magnitudes, nearly three
hundred nebulae, and globular and other clusters, _of all degrees of
resolvability_, and smaller scattered stars innumerable of every
inferior magnitude, from the tenth to such as by their multitude
and minuteness constitute irresolvable nebulosity, extending over
tracts of many square degrees. Were there but one such object, it
might be maintained without utter improbability that its apparent
sphericity is only an effect of foreshortening, and that in reality
a much greater proportional difference of distance between its
nearer and more remote parts exists. But such an adjustment,
improbable enough in one case, must be rejected as too much so for
fair argument in two. It must, therefore, be taken as a
demonstrated fact, that stars of the seventh or eighth magnitude
and irresolvable nebula may co-exist within limits of distance not
differing in proportion more than as nine to ten."--_Outlines of
Astronomy_ (10th Ed.), pp. 656-57.

This supplies yet another _reductio ad absurdum_ of the doctrine we are
combating. It gives us the choice of two incredibilities. If we are to
believe that one of these included nebulae is so remote that its hundred
thousand stars look like a milky spot, invisible to the nak