Lexington gazette. [volume] (Lexington, Va.) 1871-1962, 1905-08-09
An Explanation With Reference
To Varying Time

! An Explanation With Reference
to Varying Time
EDITOR GAZETTE My memory
was sadly at fault when l wrote,
as | did in my contribution to
The GAZETTE of August 2nd, that
the duration of daylight at diff
ferent seasons is connected with
the suns fright ascension. )" The
fact is, 1t has been many years
since studied spherical trigono-
metry and its applications to
astronomy. But recently, wish
ing to ascertain the- precise mo-
ment when the sun will rise in our
latitude during the eclipse of
August both, | turned to the
formula for calculating the hour
OF sunrise, (given on page CD of
Olmsted's Astronomy The I'M
known element in the formula is
"sine A R." But A R is not, in
this case, the arc of right ascen-
sion. The time of sunrise can be
ascertained from the formula
without knowing what A. r.
means; and l did not go through
the trigonometrioal demonstra-
ton. / assumed, without rehec-
ton, that the side A 4 of the
spherical triangle forming part of
the figure used in the demonstra-
ton was the sun 8 right ascension--
that is, the arc of the equator in
tercepted between "the first point
of Aries" and the point at which
the circle of declinatiOn passing
through the sun eats the equator.
"The first point Of Aries" or the
vernal equinox, is the point where
the equator and the ecliptic in
tersect; and from this point fright |
ascension" is measured along the
equator clear around the globe,
and may therefore amount to as
much as % hours, 80 minutes, SO
seconds. So it is manifestly in
correct to say, as l Inadvertently
did, that the arc of right ascen-
sion added to 9 hours will give
the time of sunrise in winter, and |
substracted from 6 hours will give
the time of sunrise in summer.
The formula / gave you is all
right, except that | gave the
wrong name to one of the elements.
But it is not necessary to make
any trigOnometrical calculation in
order to explain why the days and
nights differ in length at different
seasons and at different ATTITUDES.
The greater portion of the SUMS
circle of diurual motion is below
our horizon when the sun is south
of the equator, and above our
horizon when the sun is north of
the equator. From this results the
inequality of day aid hight-as
may be plainly seen by referring
to the figure and explain alton
on page 20 of Olmsted's Astronomy.
Whether the children of our
common schools would understand
the explanation, l cannot say.
But tits noteworthy shat Maury
gives no explanation of the pheno-
menon in his Manual of Geography.
Probably he thought it beyond
the comprehension of children.
Now, as Maury's Manual is the
highest text book in geography
used by the pupils of our common
schools, why should the teacher
know more of the subject than
what the text book givesE
1t is not denied that the teacher
should know more than the pupils.
The question is, how much mOre2
What is called mathematical
geography" is really part of
astronomy. Shall we require the
teacher of geography to under
stand astronomy Let US say,
yes, Then ahall we examine our
public school teachers in spherical
trigonometry because knowledge
of that branch of mathematics is
necessary to complete under
standing of astronomy This
argument will be recognized as a
reducLio Ad absurdum. But it is
precisely on a par with the argu-
ment that teachers of arithmetic ,
must be examined in algebra b.
cause knowledge of that branch
Of mathematics assists in under
standing some of the rules in {
ALBERT BAYARD TREvEY.