For we must not only have regard to the mist which
happens to be in the place where we stand; we ought also to take into our
thoughts the whole sum of vapours and exhalations which lie betwixt the
eye and the moon: all which cooperating to render the appearance of the
moon more faint, and thereby increase its magnitude, it may chance to
appear greater than it usually does, even in the horizontal position, at
a time when, though there be no extraordinary fog or haziness, just in
the place where we stand, yet the air between the eye and the moon, taken
all together, may be loaded with a greater quantity of interspersed
vapours and exhalations than at other times.
72. It may be objected that in consequence of our principles the
interposition of a body in some degree opaque, which may intercept a
great part of the rays of light, should render the appearance of the moon
in the meridian as large as when it is viewed in the horizon. To which I
answer, it is not faintness anyhow applied that suggests greater
magnitude, there being no necessary but only an experimental connexion
between those two things. It follows that the faintness which enlarges
the appearance must be applied in such sort, and with such circumstances,
as have been observed to attend the vision of great magnitudes.
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