New-York tribune., 1911-01-29

! our following the successive steps by
which this now steady Improvement was
effected. we shall pass directly to that
greatest triumph OF the makers of exact
/ instruments - the so-called ultra micro
scope.
For our better comprehension Of the
rationale which is really simple, Of this
wonderful instrument, which came into
general use only some four or five years
ago, it is necessary that we should first
. get clear idea Of the mode of action OF
| light waves. IT, while you are standing
just behind a solid screen. say three feet
| square. a second person on the opposite
side Of it shouts. the sound assails youl
| ears-is heard. That is because the sound
| waves, being ordinarily three feet or more
| in length. depending upon the pitch. easily
! close around interposed objects. these OF
| fering only little resistance TO oSclla tions
! Of such amplitude. Now. Jet us suppose
! our screen To he in a dark room. and that
on the one siGe Of it YOU place a lighted
lamp and on the other side YOU take NJ
: your position as before. Where YOU stand
VIII he in shadow. showing that the waves
Of light, unlike those Of sound. have not
closed around the screen.
the fact that the amplitude of the waves
| emanating from ordinary yellow light is
only ssixty-thousandth Of an inch. and
| such excessively slight oscillations obvious
Is cannot circumvent a comparatively i'm
mense wall placed directly in their path.
In other words. waves cannot close around
an interposed object unless their lengths
are OF somewhere near the same size as
the linear dimensions Of the object. Truly.
1t would be as illogical 10 expect q light
wave 10 circumvent even a small screen
az II would he to look for foot long water
wave on the land side of solid break
water extending for a hundred miles.
against which the tiny wavelet has lust
dashed itself
We have said that the amplitude of vbra-
tion. or wave length. of yellow light. which
Il ordinary daylight is one.sixty.thou-
sandth part OF an inch: hut II this light
he decomposed-reso into its component
colors-it will be found that certain of its
rays possess very much shorter wave
length than even that small fraction. or
all the component rays. those which are az
the extreme upper end of the spectrum.
and which are known as the ultraviolet.
nave I'm seven-one-mllionthS of an inch
the very shortest wave length. and IL is
these ultraviolet rays that are utilized ex.
clusively In the ultra microscope. Indeed
'he only difference between the ultra
microscope and the ordinary compound
microscope Ia, that while the latter illu-
mines the object 10 oe examined by con-
centratins upon il by means OF its com
densers" denses), about seven In number
yellow lisht exclusively. the former utilizes
IN the same way only the ultra violet ray,
OF light. The utra-miscroscope gets this
eneet simply by using quartz instead of
sass lenses quartz crystal having the
peculiar property OF absorbing all ravs
from an arc light. which Is ordinarily used
excepting the ultraviolet. whereas glass
apsoros the ultraviolet and gives passsge
to tho yellow rays
Inc effect however, OF this apparently
slight difference IN the mode Of action .,
the ultra microscope upon the maen,rv,n.