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% David R. Wilkins
% School of Mathematics, Trinity College, Dublin 2, Ireland
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% Trinity College, 1st June 1999.

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\centerline{\Largebf NOTE ON MR. POTTER'S REPLY}

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\centerline{\Largebf By}

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\centerline{\Largebf William Rowan Hamilton}

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\centerline{\largerm (Philosophical Magazine, 2 (1833), p.~371.)}

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\centerline{\largerm Edited by David R. Wilkins}

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\centerline{\largerm 1999}

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{\largeit\noindent
Note on\/ {\largerm Mr.~Potter's} Reply.  By\/}
\hskip 0pt plus10pt minus0pt
{\largesc William R. Hamilton,} {\largeit Esq.\
Andrews' Professor of Astronomy in the University of Dublin, and
Royal Astronomer of Ireland\/}\footnote*{Communicated by the
Author.}.

\bigbreak

\centerline{[{\it The London and Edinburgh Philosophical Magazine
and Journal of Science},}
\centerline{vol.~ii (1833), p.~371.]}

\bigbreak

From Mr.~Potter's Reply, published in the April Number of the
London and Edinburgh Philosophical Magazine, I collect some
additional facts respecting his experiment of prismatic
interference, which do not seem to have been stated in his first
account of that experiment.  In Mr.~Potter's first paper, the
stress of his objection to the undulatory theory of light seemed
to be laid on the {\it observed direction\/} of a certain
deviation; to which he opposed his {\it calculated decrease\/} of
a certain hyperbolic ordinate.  I showed that {\it this\/}
observed fact, of deviation in the observed direction (towards
the thickness of the prism), could be accounted for by the
prismatic aberration of figure, which changed the decreasing
hyperbolic ordinate to an {\it increasing ordinate\/} of a
certain other curve.  But I was of course aware that this
prismatic aberration, though a cause acting in the observed
{\it direction}, might not be energetic enough to account for the
whole, or even for the greatest part of the observed effect; and
that whether aberration was, or was not, an {\it adequate\/} as
well as a {\it real\/} cause (on the undulatory theory of light),
must depend on the comparison of my calculated formul{\ae} with
the {\it observed magnitude\/} of the deviation, of which
Mr.~Potter had not given any measure, or even any estimate.  I am
happy to have been the means of inducing Mr.~Potter to bring
forward some additional testimony on this important point: and
willingly admit, that, according to this new testimony, there
remains, after allowing for my suggestions, a large residual
ph{\ae}nomenon.

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Dublin, April~13, 1833.

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