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[[left top margin]] 135) [[/left top margin]]

[[left margin]]The phenomenon of the Horizontal Moon attempted upon new principles [[/left side margin}

Mr. URBAN,

As I was walking one evening upon an hill near this town, the phoenomenon of the horizontal moon, took up my attention. The evening was clear, and with a quadrant I measured the angle it subtended to the eye. Soon afterwards a fog arose, and upon a like mensuration I found the angle considerably less. I began to consider, whether this accident of the fog might not in some measure afford a solution of this phoenomenon, so frequently and so unsuccessfully attempted. [[underlined]] Molineua [[/underlined]] [[should be Molineaux]] in his dioptrics, [[underlined]] Smith [[/underlined]] in his optics, [[underlined]] Rowning [[/underlined]] and other sages of natural philosophy, seem to have proceeded upon wrong principles. They have endeavoured to account for the moon's magnitude in the horizon, without considering the nature and state of the medium through which we view it. Now it is a most evident principle in physics, that the vapours arising from the surface of the earth, while they are near the surface, are in a state of rarefaction, and are not in that of condensation, till they arise at the superior parts of the atmosphere. That they are rarefied near the surface is plain from their easy dissipation, when the least flux of air agitates and impells them. That they are condensed in the upper parts of the atmosphere, is plain from their formation into clouds, and meteors. If we look at the moon in the horizon, we guide our eye in a direct line over the surface of the earth, and consequently view the moon through a medium, that suffers little or no obstruction from the spissitude of vaporous particles. If on the other hand we view her in the meridian, we look at her through a dense, gross medium, in which a great part of the emissive efficacious rays are absorbed, and by a known rule in optics, where the rays that should be efficacious are less transmitted to the eye, the less will an object appear, or the appearance of an object will be less than it should be: yet we well know, that the meridional moon should appear larger, according to optical reasoning, than the horizontal, because the meridional is nearer to us by almost a semidiameter of the earth. But it will be said, how can we be said to view the meridional moon through a dense medium, when we generally see her, if at all, in a clear sky. Here lies the deceit. We think the sky is clear when we see no clouds. Clear indeed from clouds, but at the same time replete with vapours: Vapours of a different kind from those which constitute clouds, and which undergo a considerable degree of condensation. It is no unusual thing to experience this, when we look upwards in a starry night. Those coruscations in the atmosphere, that undulation made visible by the stars, those scintillations of luminous matter, vulgarly called the falling of a star, are sufficient proofs of the airs redundancy in vapours. To make the thing intelligible I have drawn the following scheme. 

[[bold]]A [[/bold]] is the meridional moon, [[bold]]B [[/bold]] the horizontal, [[bold]]D [[/bold]] the surface of the earth, [[bold]]CD [[/bold]] a space within which the superficial vapours fluctuate, [[bold]]F [/bold]] the eye of the spectator. [[diagram - drawn on the right side of the page, one vertial line with two horizontal lines intersecting to the right, labeled with the above-stated letters]] When the eye of the Spectator is directed forwards towards the horizon, the space [[bold]]CD [[/bold]] abounding with few, if any, vapours that are infinitely rare and expanded, and whose component particles consequently cause no sensitive alteration in the medium of air; unless it  [[end of page]]

Transcription Notes:
Mary Smith's cursive handwriting allows often for two s'es next to each other to appear as an "f" and "s". Thus, you would read "lefs" when the word is "less." Keep that in mind!