The Washington times., 1922-06-07
Scientific Deceivers
PROF. SERVISS EXPLAINS TWO OF THEM.N.
He Explains. Difference Between Clock
Time and Solar Time, and Expounds
Theory of RefractiOn.


April the sun would be. eight min.
utes slow by the clock. and at the
beginning of October eight minutes
fast. ~ ~. n
ON the other ~. hand. II the
obliquity Of the eciiptic alone II
that alone operated. the clock
would be together at potlis the
equinoxes and the solstices tMarcr
21, June %, September q and
December 22), while the sun would
be about ten minutes slow early
in February and August, and ten
minutes fast early in May and
November.
But putting the two things to-
gether we get the actual state Of
affairs. by which the sun and the
clock are together April Is. June
~ September ! and December "a.
From December "a until April Is
the sun is slow by the clock,
reaching a maximum Of IA min
utes 80 seconds February IL; from
April Is to June II the sun is
fast by the clock reaching a maxi.
mum Of minutes SIS seconds May
IL; from June IA to September l
the sun is again slow by the clock,
reaching a maximum OF Is min.
utes 12 seconds. July 26. and from
September. to December 20 the
sun is once more fast by the clock,
reaching a maximum of l6 min
utes IS seconds November 2.
There is source Of confusion
which can be avoided by remem-
bering that when the true sun is
ahead in right ascension Of the
mean sun. or fictitious sun, which
the clocks follow. II is further
east. and consequently must come
to the meridian later than the
fictitious sun: in other words, the
sun is then slow by clock time.
(2) The effects OF parallax and
refraction are exactly contrary as
applied to the apparent position OF
a heavenly body. The pars1laE
tends TO throw the body lower, l.
e., further from the zenith Of the
observer, while the refraction
tends to lift the body from the
horizon and toward the zenith.
Both attain their maximum effect
when the body is near the horizon
But the parallax varies inverse.
ly with the distance OF the body
from the earth. For the moon II
Is relatively large. amounting at
the horizon to about fifty-seven
minutes OF arc, while for the sun
in the same position II Is less
than nine seconds Of arc, too
slight for the unaided eye to per.
ceive. Since the horizontal re.
fraction for all bodies ranges on
the average in our latitudes from
thirty-two to forty minutes Of
arc, we see that upon the whole
the moons apparent position is
more depressed by parallax than
raised by refraction. so that her
time of raising is retarded and
that of her setting FASTENED by
about a minute.
Except in the case OF the moon
II is not important for ordinary
purposes TO consider the effects OF
parallax. but those of refractior
must always be taken into accoun
in any fairly accurate work. This
as above said. amounts ordinarily
at the horizon. to from THIRTY
two to forty minutes of arc. Thi'
exceeds the apparent, or angular
diameters Of both the sun and th'
moon, which have nearly the SAM
apparent size, so that either OF
them when rising or setting is
usually lifted by about the amount
Of it's own diameter above its true
place. II follows, of course, that
when abe sun has actually set II
may still be wholly in sight. rest
ing it's lower rim on the horizon.
Several circumstances cause va
riations in the amount of the at
mospheric refraction. 1t varies
with the temperature of the air
and with the barometric pressure
The colder the air the greater tne
refraction; the .rarer the air the
less the refraction. The two effects
may occasionally be blended in
such a manner as to entail extraor-
binary refractive conditions. pro.
ducirg very deceptive appearances.