Spirit of the age. [volume] (Woodstock, Vt.) 1845-1913, 1904-12-03
non N the top story of an un


mechanical occupations. The resi-
dence is that of Max Kahler, famous
among scientific men who employ OPP
teal instruments as an adept IN the
difficult art OF lens making, Mr.. kah'
Ter has made some OF the most delicate
lenses in use ut the Naval Observa-
tory, the Astrophysical Observatory OF
the Smithsonian Institution, and other
scientific establishments throughout
the country, while number OF fine MI
croscopes, together with large pro-
portion OF theOdolites employed by sur
veyors, owe their excellence to the
lenses which he has turned out In his
simple little Worship.
A person does not necessarily have
TO be versed In scientific matters TO re-
alize that the accuracy Of the images
transmitted by such instruments as
the telescope, camera, microscope, etc..
depends entirely upon the perfection or
the glass surface upon which the I'M
age is received and through which 1t
Is conveyed to the human eye or the
sensitive plate. We are all acquainted
WIN the wavy looking glass, when
may be purchases for few cents, and
which represents the human face dl-
vine" most fearfully and wonderfully
distorted. Between such a glass as
this and one that would faithfully re-
feet an object with nearly absolute
axactness, there Is, as far as regards
mere cost, q difference Of several hun
dred dollars.
But the value to the scientist cannot
he over estimated Of an exact plane or
curved surface of glass. The former,
especially, principally required in mir
.ors for receiving the suns image, is.
as Mr.. Kahler will explain, one Of the
incest achievements in the making or
optical Instruments. In illustration or
this fact, Mr.. Kahler pointed 70 disk
IF glass, sixteen inches in diameter.
which vas conspicuous upon dusty
work bench. This was to be made in
to a mirror for one Of the instruments
IF the astrOphys steal observatory OF the
Smithsonian Institution, and the work
which was TO be done upon 1t, ana
which would occupy some six weeks
IF persistent labor Of the most skllful
and labOriOus description, was TO put
A perfectly smooth or plane surface
upon it. When this was accomplished
The unpretentious piece of glass would
De worth $1,000. This may appear
strange to a person accustomed to re-
gard the French plate looking glass IL,
his room as having = perfectly plane
surface and rejecting his image with
absolute exactness. TO all practical
.ntents and purposes, indeed, the latter
object is accomplished; nevertheless.
he surface of the glass Is a long way
from being plane In the scientific
meaning of the word, and In the re-
auirements of optical Instruments
In order to realize the ,alne OF these
accurate mirrors. one has only to ex-
anime the method employed for taking
A photograph Of the sun each day at
the Naval Observatory. The image
If the luminary is first received upon
mirror and thence transmitted to the
mouth Of e-ea..sro.-.Hheeo- ~rrp PRIV
tographs disclose, with the most ex-
luisite minuteness, the structural fea-
lures of the suns 'envelope," as the
luminous mass surrounding it has
been termed. The so-called sun spots,
for the observation Of which these pho
tographs are principally taken. are
shown in wonderful detail, the pecu'
liar tibrous structure attributed to jets
If fame and the different densities
being clearly distinguishable. 1t is
scarcely necessary to observe that II
the mirror transmitting the image In
the first place We're not perfect
plane, or something very near 1t, the
picture, depending for Its value upon
such minute detail, would be distorted,
confused, and absolutely worthless for
scientific purposes.
How do you test the surface Of the
glass in order to ascertain whether OF
not it is n perfect plane?" Mr.. Kahlei
was asked.
For answer, the worker in optics took
two pieces Of plate glass. These
nse merely to Illustrate he explained
"Of course, these are by no means
plane surfaces, though they are about
us much SO as will be found in the or
binary fire mirrors of commerce.
use a plain surface for the purpose OF
actual testing, which place over the
surface l am working on just as
place this piece of glass over the
other. Then l take piece Of meta
screen and dip it in salt mixed witt
some intia hmable liquid, and so get tie
yellow sodium rays. Now, after plac
ing this simple apparatus il the trl
pod here, l hold the two pieces Of
glass so as to catch the sodium rays
and you will notice the innumerablt
lines, black and white alternately, that
traverse the surfaces of the glass IL
all directions. These lines, in accu
rate planes, would be about half al
inch apart and would be parallel
whereas, here you see them running iI
curves, zigzags, and every other way
and very close together. The fewer Of
these lines there are, and the more
nearly parallel. the more more accu
rate the plane"
Mr.. Kahler called attention to a Gu
rious class of work which he had done
for the astrophysical observatory o.
Smithsonian by producing prisE
inclosed in Theoretically sealed glas!
jar. This prism was, apparently, o.
the clearest crystal; in reality 1t wa!
Of peculiar quality Of rock salt oh
tained from a certain mine in Russia
The reason for employing rock sal
in transmitting the rays Of the sun II
the non-absorptiOn Of heat by that sub
stance, while, ON the other hand, it
absorption Of moisture rendered IT.
surface liable to be destroyed by ;
change in temperature or contact will
the least dampness. These prisms arr
made in room of the astrophysica
observatory, the temperature of which