The enquirer. [volume] (Richmond, Va.) 1804-1815, 1811-05-10
To THE EDIroR OF TIE ESoylRsR.

The essays upon Light, read to the institute
OF France, by Messrs. Aialus and Blot, which are
contained in the Paris Moniteurs, of TIE 18th &
f4ih March last, that received from you, re-
late to discovery more interesting than any
which has been made in the scirnce of optics
since the days of sir Isaac Newton. To under
stand the nature and history of this discovery
II is necessary that the reader should be scquain-
ted with the subject OF a previous essay read by
Mr. Mal's, TO the institute in 1903, rs also one
by Mr.. La Place on tue 3Oth OF January, 1909
have neither OF these essays by me, but l have
an abridgment of them by the editors Of the
Quarterly Review, which is sufficient for the pre-
sent purpose.
The two principal theories of light, which
have divided the philosophic! world, are those
OF Huygens u Newton.--The former is we'll
Known TO have explained the Phenomena OF
light by an undulation resembling that of sound,
produced by luminous bodies in subtle fuiu,
dispersed throughout the universe, while New
ton supposes thai light IL Il real emanation from
luminous bodies Ofthe phenomena of light &C.
morally observed, the. greater part will admit OF
an explanation equally satisfactory from either
OF the theories but the great name of Newton,
was the cause OF the Huygenian theory sinking
into oblivion for almost a century. Within the
last ten years, however, the theory of Hnygens,
seems again-to be recovering its former reputa
tion, and that OF Newton, giving way to the truth
of eXperiment--Thee extraordinary phenome-
non of Iceland crystals, or OF those crystals,
which are called doubling crystals, presented
fact difficult to be explained by either theory
u was well known to Huygens well to
Newton, that a ray OF light transmitted and d.
vded by one piece OF Iceland crystal, was Ell
ther suodisded, or not, by second piece, &C
cording TO the relative position OF the two crys
tails so that it we looked down through both
OF them. and the obtuse angle of one was situa-
ted on the north side of the ray, and that of the
other on the north east side, four images ofany
object would be seen; and only two ii The OBJ
fuse angle OF the second, was either on the
north side or on the enst On the above fact tile
editors otthc Quarterly Review, remark as
follows, No vi, page 473
" Now in the simple Hueenian theory of an
unduiation resembling that of sound, the ray
must be alike On every side, as well after as be-
fore Its passage through The first crystal nor
Can be imagined how its affections can be diff
terent with respect to north & north east, or to
any other points of the compass and this was
advancedby Newton as an objection, which
Huygens had not been able 10 overcome We
venturea to'suggest on u former occasion, that
the curvature of the undulation, or in Other
words, the divergence of the light, might posi-
bly, be different III different directions now
Mr. Maiuss experiments are precisely such as
90 afford an answer to this suggestion since
Shey shew that the divergence absolutely UNI
concerned IN The phenomena, and that q similar
division OF the light may be produced by simple
reflection from plane surface, where no change
OF divergence takes place in any direction"
In page 329, Of No. w, in reviewing an es-
Say OF Mr.. La Place on the phenomenon of the
iceland crystal which was read TO The institute
on the 5Oih of Jam 1S09-They observe "this
iaw was experlmentaiiy demonstrated, and very
elegantly applied To the phenomena by L., first
discorerer Huygens but having been suggest
ed to him by hypothesis, which was not uni
versaly adopted, it was rejected or neglected
by his antagonists, without any accurate inyes-
md he log tI.
iosoPher OF that age, or Of any age, having been
opposed to it, 1T remained forgotten for almost
century. Nor is this the only instance in which,
even within the limits of the physical sciences,
high authority has been suffered to prevail a.
gainst unassumIng truth--Mr. Hauy is the
first OF the later observers who remarked, that
the true law of extraordinary refracton, was
much nearerto the Huygenian law, than to that
which had been substituted for it by Newton
Some time afterwards DR.. Wollaston had made
number OF very accurate experiments, with an
Apparatus singularly well calculated to examine
the piienomena, but he could find no genera,
principle to connect them, until the work of
JIuygens was pointed out to him. he was then e.
nabled,by means OF the Huygenlan law, to reduce
bis experiments to a comparison with each other.
L ia communicating them to the royal society, he
remarked tnat =" the obique reiraction, when
considered alone, seemed to be nearly as well
explained as any other optical phenomena -
Here the matter rested, until Mr.. Malus made
the experiments which have led to the present
paper.
The editors of the Quarterly Review
then give the following extract from the ESSAY
OF Mr. La Place" Mr.. Mslus has lately com
pared the Huygenian law with very great
number OF experiments made with extreme pre
risoR, on the natural and artificial surfaces of
the crystal, and has found that the law agrees
exactly with his experiments, so that it must
he placed among the most striking results OF
physical observation. Huygess had deduced IT
an q very ingenious manner, from his hypothesis,
respecting the propagation OF ILL., Int, which he j.
imagined to consist in the fluctuations of an ethe.
RAJ huId This great geOmetTician supposed the
velocity OF the calculations the ordinary uans-
P}fent mediums, to be smaller than in vacu-
sln', and to be equal in every dire ctOn III the
Iceland crystal lie imagined Two distinct spe
cies OF fluctuations The velocity in the air be-
InS tue same m all directions, IN the other yari.
able, and represented by the radii of an elliptic
Spheroid, having the point Of incidence for ITS
cenre, and its axis being parallel to that of the
crystal that is, 10 the right line which joins
the two o6tase solid angles of the Rhomboid.--
iluygens Goes not assign any cause for this varie-
fy vi unduistions and the singular p.Iunomena
exhibited by the light, which passes from one
portion or the crystal into another are inexoH
cn6Ie upon his hypothesis. This circumstances
together with The great difficulties presented by
the undulatlng theory of light in general, has n
pliers, to reject the law Of refraction founded ON
the HuygenIan system. But since experiments
have demonstrated the accuracy of this remark
10 Iusn,