es may vary the judgment
made on the magnitude of high objects, which we are less used to look at:
but it does not hence appear why they should be judged less rather than
greater? I answer that in case the magnitude of distant objects was
suggested by the extent of their visible appearance alone, and thought
proportional thereto, it is certain they would then be judged much less
than now they seem to be (VIDE sect. 79). But several circumstances
concurring to form the judgment we make on the magnitude of distant
objects, by means of which they appear far larger than others, whose
visible appearance hath an equal or even greater extension; it follows
that upon the change or omission of any of those circumstances which are
wont to attend the vision of distant objects, and so come to influence
the judgments made on their magnitude, they shall proportionably appear
less than otherwise they would. For any of those things that caused an
object to be thought greater than in proportion to its visible extension
being either omitted or applied without the usual circumstances, the
judgment depends more entirely on the visible extension, and consequently
the object must be judged less. Thus in the present case the situation of
the thing seen being different from what it usually is in those objects
we have occasion to view, and whose magnitude we observe, it follows that
the very same object, being an hundred feet high, should seem less than
if it was an hundred feet off on (or nearly on) a level with the eye.
What has been here set forth seems to me to have no small share in
contributing to magnify the appearance of the horizontal moon, and
deserves not to be passed over in the explication of it.

74. If we attentively consider the phenomenon before us, we shall find
the not discerning between the mediate and immediate objects of sight to
be the chief cause of the difficulty that occurs in the explication of
it. The magnitude of the visible moon, or that which is the proper and
immediate object of vision, is not greater when the moon is in the
horizon than when it is in the meridian. How comes it, therefore, to seem
greater in one situation than the other? What is it can put this cheat on
the understanding? It has no other perception of the moon than what it
gets by sight: and that which is seen is of the same extent, I say, the
visible appearance hath the same, or rather a less, magnitude when the
moon is viewed in the horizontal t