Year: 1872

the Phenomena of its Atmosphere" gives
some very fresh illustrations respecting
our solar neighbor. The distance to, aud
the weight and destiny of, that independ-
ent luminary are thus sketched


The first thing to be ascertained if pos
sible with reference to heavenly body is
its distance. A knowledge of this is es-
sential to any determination of its real
magnitude and weight, and these must be
known before we can form correct idea
of its physical constitution and modes of
action.


Did time permit, it would be interesting
to explain some Of the many methods by
which the distance is determined, and es-
pecially to recall the course by which was
discovered and corrected an error Of more
than three per cent in the value univer-
sally accepted less than twenty years ago.
At that time the distance was considered
to be about ninety-fve millions of miles
it is really less than ninety-two millions.
This is the average distance, but the sun
Is some three millions of miles nearer on
the first Of January than on the first of
June.


While there is very little doubt however
that the suns mean distance Is between
nlnety-one and ninety two millions Of miles,
the margin Of error is still pretty large
probably half million of miles one way
or the other,-and it is in hopes Of adding
greatly to the precision of our knowledge
that astronomers are now looking forward
with so much interest to the coming trans
its Of Venus in the years 1874 and lSs2.
These phenomena, usually Y occurring about
twice in each century, furnish the most
accurate means of asoertaining the solar
parallax, upon which the calculation of
the distance depends, and the different
governments are already taking measures
to provide for the necessary observations.
am sure you will all join me in the wish
that our own country may not be behind
the rest. L do not suppose that In stating
the distance Of the sun as nintey-two mil
lions Of miles | have communicated 10 you
any real notion. Probably l might Just
as well have said ninety-two billions The
conception IS too vast to be fairly grasped
by the human intellect, but perhaps one or
two illustrations may assist in the matter


If on some intermundane railway be-
tween the earth and the celestial metropo-
lis the Pilgrim Fathers had started from
the sun at the same time when they really
left England, and if they had travelled by
special express at the rate Of forty miles
an hour, without stops, since there could
be no way stations on such a line.l they
would not yet have arrived, nor would
their train be due until lsS3-363 years
upon the road. At the present time, with
only eleven more years to 20, they would
still be sixteen times as far distant as the
moon; so remote that the earth would
be to them only brilliant planet, Of about
one fifth the moons diameter. 4 cannon
ball, moving straight on unretardei with
its swiftest speed, could not make the Jour
ney to the sun IN nine years. If sounds
could travel through the celestial spaces
at the same rate as in our air, then the
thunder Of a solar storm or the report OF
an explosion such as occurred last Septem-
Der might reach US in a little more than
fourteen years.


And yet across this tremendous chasm
the sun exercises his lordship and performs
his service every pulsation Of the solar
surface is instantly responded to upon the
earth The distance Of the sun once
determined it is very easy to ascertain his
diameter, which comes out eight hundred
and sixty thousand miles, nearly one hun
dred and nine times as great as that of
the earth. Representing the earth by
boys ball two inches in diameter. the sun
on the same scale would be something
more than eighteen feet through. If the
earth were placed al the center of the sun
the moon would be far within his surface,
so far indeed that there would be room
within it for another moon almost as far
again from the earth. In bulk it would
take more than a million and a quarter
earths to make a globe of equal size
Knowing the distances of the sun and
moon. the lengths Of the year and Of the
month, it is easy, by methods which L
cannot now stop to explain, to ascertain
what is called the mass of the sun-that
is to say the number of tons of material
in it. or, since the ton would be a ridicd-
lousy small unit for such a measurement,
number of earth-weights in it.


The sun weighs nearly three hundred and
twenty-five thousand times as much as the
earth Recalling the fact that it is one
million two hundred and fifty thousand
times as bulky, it is of course evident that
bulk for bulk it is much lighter tnas the
earth or, to speak technically, its densi-
| ty is only about one fourth that of the
| earth-about one and one half times that


of the water. This is a most important


and suggestive fact when taken in connect.


ion with this other fact, that on the sun


the force which attracts bodies to his sur.
face, the solar gravity, is about twenty


eight times as great as terrestrial gravity
! On the earth body let fall drops about


sixteen feet in the first second on the sun


it would fall four hundred and fifty feet


The stately swing of the pendulum of al


astronomical clock would at the sun become


quiver more rapid than the vibration o.


the quickest watch balance. a graceful


lady, whose sylphlike form here would


hardly weigh one hundred pounds, if car
ried to the sun would become as unwieldI


as an elephant, or rather would be crushed


by her own weight. Her airy little heaC


alone would weigh nearly two hundred


and fifty pounds.


Now it would at first seem that th


remarkable lightness of the solar substanc,


and the great power of solar gravity car


be reconciled only by supposing the sun t,


be in the main gaseous mass, a mer


cloud of vapors toward this conclusion


also many other facts converge, such as tn


intensity Of the solar temperature and th'


peculiar motions observable upon his sur
face. At present this may perhaps b.
! regarded as the prevailing opinion anon
men Of science-only an hypothesis, how


ever, not yet by any means fully establish
ed. 1t seems to have been first seriousl,
proposed and defended by Secchi, an
/ and afterward adopted and more cogentl,


enforced unon different grounds hU n