Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-03-29

not measuring the heat of the match but thu
reradiation of the heat from the metal"
These reradiated rays are the ones which tiF
device uses and the all-weather sextant IL
founded upon the principle of using the rays on
the visible side of the cloud or fog to focus on
the sun. It is in two parts one the actual SEX
tant and the other amplifier. The sextant
portion is similar in appearance to the ordinary
sextant but it operates in an entirely different
manner.
Before the special reflector concentrates tho
invisible infra-red rays and focuses them on the
detector, gelatin screens intercept the light and
filter out all the rays except those OF th0
longer infra-red radiations
Flexible wires carry the infinitesimaI current
which has been generated from the sensitive
detector to a special ampliher and the ampl-
fed current is then carried back by another
wire to an indicating scale on the sextant.
The detector IS so delicate that it will pick
up one microvolt-a millionth of a volt-and
the ampli1er powerful that it viii amplify
100000 times. Thus far Mr.. Macneil has not
found 1t necessary to use the full range Of the
amplifer. In the low visibility Of ordinary bad
weather during the tests it was only necessary
to step up the detected current about $500
times.
According to the inventor the amplifier win
not be affected by the movement of the ship.
In order to study the effect of vibration upon 1t
he has taken the instrument up in an airplanO
and operated it efficiently without disturbance
of its accuracy.
WHAT makes possible the success Of the ALL
weather sextant is the fact that the longer
infra-red rays are reradiated in a direct line
from the short waves on the other side Of the
clouds. Therefore, when the indicator shows
that the reflector has been focused ON the
maximum point Of infra-red rays, it gives
scientific evidence that the sextant is focuses
directly upon the sun.
no ant io In fho 4NMH
naVigators have been using such instruments
since the primitive cross bar came into umR
some time in the fifteenth century, except thaD
instead of viewing an image of the sun, tho
navigator views the indicating meter which
electrically records the fact that the instruments
Is in focus.
To insure precision of the focus on the re-
Hector the rays are required to pass through
diaphragm having an aperture Of about Ona
millimeter, which is about the diameter of tina
sun as it would be if it shone down unobscured
upon the reflector at that distance. The in
strument is accurate to about 20 minutes OF
latitude according to the inventor.
Mr.. MaeneIS first experiments, made at his
home in Huntington, Long Island were conduct
ed upon an instrument imbedded in a concrete
base and so sensitive that it registered the heat
OF mans hand placed near it. His present
device contains an element similar in principle
TO the thermo-couple used by astronomers to
measure the heat Of distant stars
With the new form of sextant, says the in
Ventor, the navigator can get the true altitude
OF the sun at any time without difficulty as long
as the sun is above the horizon The instrl-
ment was made in its present form with the
familiar Sextant attached so as not 20 break
Zoo sharply with the practices of the past and
the present. and not to stir up the prejudices
Of old sailors who have been using sextant
readings for q lifetime
At the present time addition of the reflector