The enquirer. [volume] (Richmond, Va.) 1804-1815, 1811-05-10

ty. But there is condition which becomes me-
cessary in the case Of extraordinary refraction,
which is that the velocity ut the ray light in
the medium must be independent of the 7,ian-
ney IN (Which At has entered i., and must be de-
termned only by its situation, with respect to
the axis of the crystal, that is by the angle
which the ray forms with line parallel to the
axis +" L have found that the law ofextrsordin &
ry refraction, laid down by tIuy gems, satisfies
this condition, and agrees at the same time with
the principle of the least action; SO that there
IS no reason TO .!ou6t thar il IS driced from fhe
berdtfon Of attractive and repaISiVe forces, of
which the action is only sensible at nsenshle
distances.-The expression OF the velocity. TO
which my analysis has conducted me shords pl-
lsd6le datum Tor determining he nature OF these
forces this velocity being measured by frac-
tion, OF which the numerator is unity, and the
denominator the radius Of the spheroid which
IS described by the light the velocity in a vacu-
um being considered as unity. The velocity Of
the ordinary ray, in the crystal is equal to unity
divided by the principal axis of the spheroid, &
IS consequently greater than that of the extraor
binary ray the difference of the squares of the
Two veioc'tes being proportional to the square of
the sine OF the angle which the later ray makes
with the axis & this difference represents that
Of the actions ct the crystal on the two kinds of
rays.-Accord'ng to Huygens, the velocity of
the extraordinary ray, in the crystal, IS simply
expressed by the radius of the spheroid; conse-
quepty his hypothesis does not agree with the
principle ofthe least sctioni but it 10 renIa,ka
bic that it agrees with the principle of Fermat,
which is, that light passes from given point
without the crystal, to given point within it,
IN the least possible time for it is easy to see
that this principle comedies with tina, of the
least acton, IT we mvert the expression OF the
velocity. Thus both Of these principles lead US
to the law of extraordinary refraction, discover
ed by Huygens, provided that, for Fermat's prin.
ifyD .tye .ral-
spheroid, as representing the velocity, and, for
the principle ofthe least action, this radius be
made to represent the time employed by the
light IN pass ng through given space If the
diameters Of the spheriod are equal. the figure
becomes sphere, and the refraction resembles
ordinary refractions,o- that in these phenomena,
nature, IN proceeding from what is simple to
that which is more complex, takes the form, of
the efGpsis next to that of the circle, as IN tie
motion and figures of the heavenly bodies"
mus tar VI. La Place on the experiments of
Mr. Malus. The editors ofthe Review in page
473 No g give the following outline Of the dis
covery of NJ Malus.
" Suppose the altitude Of the sun on the me-
| r'dian to be 100 10, and plate of glass not sill
vered, 10 be so placed, AS to reflect ray of his
| light directly downwards then If a second
plate be fixed below and parallel it, this plate
Will again reflect the descending ray into a di-
| rection para'l to the original one and nothing
remarkable will happen But if we turn round
this second plate, without ring its inclination
to the horizon as it faces the east or
west, 1t will no longer reflect any part of the
'ight, either from IFS INTERIOR from its poste-
rIor surface, when however, it has made half
revolution, and fronts the south, it will again
reject the usual proportion of the incident light
and IN the intermediate positions, the reflection
~iiioe more or less perfect, as the reflected ray
approaches more or less to the plane of the meri-
dian II now instead of the second plate, we
place piece ct Iceland crystal with its p-inci-
pal section In the plane of the meridian, the
whole OF the reflected ray will be transmitted by
the ordinary retractions but if we turn TO und
the crystal till the direction of its principal
non became east and west, the ray will now be
subject to the extraordinary refraction only ;
and IN all Intermediate situations of the crystal
II VIII be divided into two positions. NJ Malus
has entered into several more particular details,
respecting the results of similar experiments UNI
der various circumstances but they do not add
| materially to the interest of the facts as TINS
simply stated"
" The angle coincidence, at which this mo.
dihcstion takes place the most completely, is
different tor substances of different densities for
| water it is $50, IS /; for glass $40 IS, and for
Iceland crystal 500 80. Black substances, such
| as polished ebony, have similar property but
| metals are entirely destitute of it-When q
modified ray is reflected by metallic mirror
SO as to continue in its principal section, or to
proceed IN plane perpendicular to it, it still re-
tains its properties but fits new direction be
equally inclined to both these planes, its modi-
fcation will be destroyed"
M Malus has discovered, that in all doub-
ling crystals, one OF the refractons is always of
the extraordinary kind and that whether we
employ carbonate of lead, sulphte of barta,
crystazed sulphur, or rock crysta al, the modifi-
cations which take place are precisely of the
same nature. He has also ascertained, that the
internal reflection of the doubling CRYSTALS eau
ses, IN general, further subdivision of the light
reflected"
This appears to have been the state of the j,s-
coveries OF M. Malus on the 18th of last March,
Whsn ne read another paper to the Institute
containing an account of additional experiments
which he had made relative to the same sub
lect. This paper is reported in the Moniteuy
OniVersel of Paris, the 18Th of March-M. Ma
lus commences HE memoir by the recapitulation
OF ms former experiments nearly in the same
words as IN the Quarterly Revie w, which have
quoted above and then proceeds
y we therefore see that ray of vertical light
when falling upon transparent body, will OBJ
serve certain law, wheH the xeflectinp surface
OF the body is turned towards the North and
South, but will be affected in contrary man
ner when the surface is directed towards the
East or the West; although in other respects
the faces of the rejecting body preserve the
same angle with the incident ray, viz. an angie
oil $50, rs. These appearances would induce
is to believe, that light acquires under those
circumstances properties independent of its di-
rectlon, with respect to the surface which re-
fleets it and relative only as to the sides of the
vertical ray winch are the same with respect to