New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1872-12-23

1.-THE light in the circles as represented in the diagram,
was white. In the middle Of each the strip OF ourma
line was represented In by green, in the other by
black image. The tourmalne rotated on its cen
ter and when the two images formed horizontal iDe
they had each partaken OF the others character 80 as
both to appear of darkened green When st further
rotated the images entirely interchanged colors,l
Given two beams transmitted through Iceland spar.
determine Instantly by of plate OF tourmaline
the directions in which the ether particles ybrae In the
any position whatever. minutes trial with the tour
maline would enable you TO determine the position
you would at once infer the directions OF vibration
Further, the two beams from the spar being thus
pOlarized II they be received upon plate OF glass at
the poarizng angle one Of them Will be reflected the
previous knowledge. Let test the conclusion by ex
pertinent. You will observe that reason is Justified
A TRANSPARENT FILM OF MICA TURNS DARKNESS INTO
LIGHT.
have said that the whole Of the beam reflected from
glass at the poarzing angle IL Ipoarzed; word must
now be added regarding the larger portion OF the light
which IS transmitted by the glass. The transmitted
beam contains quantity OF poarlzed light equal to that
of the whole transmitted light By taking two plates of
glass instead OF one augment the quantity ofthe ans
nhed pOarized ght and by taking bundle OF plates
we increase the quantity as to render the transmitted
beam, for all practical purposes perfectly polarized
means of furnishing poarized light
Let US push our reasoning still further When the
tourmanes crossed the space where they each
other black But have seen that the least obquy
or crystals 10
both Now suppose, when the two plates are crossed
that nterpOse third plate Of tourmaline between
them with its axis Obique 10 both. portion OF the
light transmitted by the frat plate will get through this
intermediate But after 1t has got through its plane
of vibration is changed 1t is longer perpendicular 10
the axis Of the crystal IN front Hence 1t Will get
through that crystal Thus, by reasoning infer that
the interpOsihon OF third plate Of tourmlline
will in part abolish the darkness produced by the
ing OF the other two plates have not third plate OF
tourmaline but the tale mica which you employ In
your stoves convenient substance, which acts
in the same way. Between the crossed tourmanes,
Introduce film OF this crystal You the edge OF the
lm slowly descending, and as IL desoends between the
tourmaines light takes the place Of darkness. The
darkness In fact seems scraped away as II 1t were some
thing material.
TThe Interpolation Of what evidently perfectly
transparent film OF mica had extraordinary effect.
Tt seemed strange. despite all explanation, that this
transparent image, visible only by few streaks Of
color and is nonransparent edges passed upward till
struck the dark spot the darkness disappeared before
IT, Again and again the lecturer introduced and with
drew It, amid much applause. 1t lifted the darkness
s ~ IL were something solid that raised by the edge
| OF the mica and pushed out OF the way.l