Phenix gazette. [volume] (Alexandria [D.C.]) 1825-1833, 1829-01-28
JOURNAL OF SCIENCE AND ARTS.

JOURNAL OF SClENCE AMI AM ..
We have been waiting, several days, for room
and time to enable US to present an analysis OF
the last number of Silliman's Journal, but the
desired period has no, yet arrived. We can
now only entreat the attention Of the public to
a work so entertaining and useful, and repeat
our opinion ,ba, it is worthy OF all the patrons
age il receives, however extensive that may be.
A number OF articles are marked either Tor
abridgement or insertion entire, but we have
space now only for the three short paragraphs
annexed, furnished by Benjamin Hallowell Of
Alexandra, D. c. Bssion Courier,
On the blue appearance Of the hedUenS.
The cause Of the blue appearance Of the hea.
vens, l have never seen satisfactorily explained.
I conceive it to be occasioned by our looking
at the dark vaeuiiy beyond our atmosphere thro'
an Illuminated medium. Were there no At
mosphere, il is universally admitted the appear
ance would be perfectly black, excepting ~ the
particular direction Of the sun or some other
Of the heavenly bodies; and since the atmos-
phere is transparent, this blackness (if may
use the expression) must be seen through it,
only somewhat modified by the rays Of ligh,
reflected by the atmosphere to the eye, from
the direction in which we are looking. For
this reason, the clearer or more transparent the
atmosphere is, the darker is the appearance Of
the heavens-lhere is then less ligh, rejected
by the atmosphere to the eye. In the zenith
the appearance is always darker than nearer
the horizon; and from the tops Of high noun
tains, the heavens in The zenith appear nearly
black
On the twinkling ofthe stars, and the
deception az the Number Visible to the naked
eye on clear srening. 1t is familiar fact, that
if person take a stick with one end ignited,
and cause the igni,ed end to revolve swiftly.
light. ffthc circle be Increased in size, or ii
the igniled end be made 10 revolve more Slow
ly, the circle may be made to appear much
brighter on one side than on the other, or il
may appear bright on one side and entirely
broken on the other. The twinkling of the
stars and the deception in the number Of stars
visible to the naked eye on . clear evening, is
somewhat similar 10 this 4 fixed star having
no visible diameter, only one stream Of the rays
OF light that proceed from il can enter the eye;
and since the fixed stars are at such All i'm
mense distance, the particles Of light from one
OF them tina, would fall upon SO small a surface
as the pupil OF the eye, must be at considera-
Die distance from each other. When therefore
particle Of light from fixed star falls upon
the eye, il produces a vivid impression; this
impression becomes gradually DINNER, until
another particle arrives, producing vivid inns
preston again. This causes the i,Vinkling.-
Here the circle is unbroken-another particle
arrives, before the impression made BY the for
mer one has entirely vanished But the parli-
eles OF light which proceed from more distant
stars, fall upon the eye at 100 great intervals TO
keep up continued image. Hence when
particle of light from one of these stars fall
upon the eye, ii produces perception Of star;
but when we endeaSor to contemplate this star,
il is invisible, because the image formed has
vanished, s. another particle has not yet arriv.
ed TO renew il. In this way we are led TO sup
pose there are more stars visible, than upon
examination we 6ad.
y The only cause why telescopes enable US 10
see stars that are invisible 10 The naked eye, is
that they concentrate the rays from so large
surface, as TO keep up continued image Of The
star.
On the cause ofhal during ,Oarna wea-
tier. Large hail frequently falls during very
warm weather, which we have had repeated
instances of, the past summer. This pheno-
menon occurs only when there il an excessive
accumulation Of electricity in the atmosphere,
and il may be accounted for in the following
manner. Two highly charged clouds in oppo
site electric states, coming within the electric
influence of each other, displace the air from
between them 50 as to form passage for the
electric fluid. while The moisture remains
This sudden displacement of the air produces
such degree Of cold, as not only to freeze the
vapor, forming the nucleus Of ,hs hail, but 10
reduce the temperature OF that frozen vapor
far below the freezing point. When therefore
the warm air comes in contacI with this frozen
vapor, the moisture is precipitated upon it and
freezes. In this way the hail is increased as il
falls to very great size.
Sometimes the temperature Of the hail is so
raised before il reaches the ground, by the con-
start precipitation Of moisture upon it, that it
Is melted, and tails in extremely large drops Of
water.