The Portland daily press., 1880-02-05
Astronomy,

The lecture on astronomy, delivered by Mr..
Harrington McIntire of Boston, at Reception
Hall last evening drew large and apprecia-
tive audience, who were very much pleased.
Mr.. McIntire has capital voice, an animated
style and his illustrations by the stereopticon
We're excellent. The lecture was devoted
principally to the solar system, which the
speaker said was but very small part of the
universe, only vestibule to the great cathe-
dral, though its diameter is six thousand mil
lions of miles. 1t consists of the sun, eight or
nine planets with their satellites, a consider
able number of comets, and perhaps two hun
bred asteroids; and the innumerable shooting
stars may be considered as part of the system
The solar system is isolated from the stellar
worlds by an extent of space totally beyond
comprehension measured by any other scale
than the velocity of light. Eight times round
the world in one second is about the speed OF
light. The sun is simply star, and at the dis
lance of other stars would appear likewise,
and yet if tunnel led from side to side through
the centre of the sun, train of cars moving at
the rate Ell five hundred miles per day would
require four and half years to pass through.
Mr.. McIntire took up the several planets
separately; first defining planet as a body re-
volving round the sun, and shining by retlec-
ted light. Aside from the eight well-known
principal planets-in order OF distance from
the sun, Mercury, Venus, the Earth, Mars,
Jupiter, Saturn, Uranus, Neptune-two as
tronomers assert they have seen an interior
first planet, which they name Vulcan, inside
the orbit of Mercury. The asteroids, small
planets, outside the orbit of Mars and inside
that of Jupiter, are in proportion to the others
very minute, varying from fifty or sixty to
four hundred miles in diameter, The lecturer
devoted considerable time to the details of the
size of the several planets, their distance from
the sun, periods of revolution, and other
characteristics
Mars has been more narrowly observed than
the other planets. being at times nearer than
any other, except Venus. Its general charac-
teristics are more like those of the earth than
are those of any other planet as to the distance
from the sun, and inclination of its axis. The
best telescopes show accumulation of snow and
ice near its poles and by their aid the surface
OF the planet has been mapped out with fair
probability, and is unlike that Of the earth in
comprising no great continent and no immense
ocean unbrok en- by large masses of land. The
land is multitude of large islands, and the
ocean is series of Mediterranean seas. The
recent discovery of two satellites of Mars was
noted, and the inner one has SO brief period
of revolutions that to the inhabitants of Mars
it rises in the west and sets in the east. The
nature of Saturn's rings was considered, and
the lecturer gave his adherence to the theory
that they are not solid as formerly was sup
posed, but more likely composed of cloud Of
minute satellites 1t appears from some data
that Jupiter and Saturn have considerable heat
of their own, and the lecturer thought that
they might radiate heat enough to produce
sensible effect on their satellites
Some time was occupied in an explanation
of the 'Ptolemaic system and that of Tycho
Brahe, each of which had its long day as the
accepted theory of the world. Mr.. Mc1ntire's
diagrams illustrating the theory of eclipses
the shadow of the earth obscuring the moon,
and the moon itself obscuring the sun-the
cause of tides, the phases of Venus, and the
movements of the principal planets, were very
interesting. The sun being SO much larger
than the moon, the moons shadow tapers off
as it extends towards the earth and therefore
a solar eclipse is visible in only limited sec
ton of the country; but a lunar eclipse can be
seen over one-half the earth's surface
wherever the moon is above the horizon so,
though elipses of the sun are more numerous
not so many are visible at any one ploce
When the moon is further than usual from the
earth, the shadow comes to point short of
reaching the earth, and where the eclipse is
central it is annular; that is, the moon appears
smaller than the sun, and at TIE moment when
the centre of the moon and the centre OF the
sun coincide, ring or annuluS of the sun Is
visible around the edge of the moon. The
cycle of eclipses is Is years, II days, at the end
of which time a new series of ecipseS similar
to the former, and at the same intervals COM
mences. There are 70 eclipses in cycle, II of
the sun, and 90 of the moon.
Tides are caused by the attraction of the
sun and moon on the water and the earth.
Every material body attracts every other, in
proportion to its weight, and in inverse pro-
portion to the square of the distance So the
moon and the sun pull some of the water round
to the side of the earth next to them, and Gre
ate tide on the opposite side of the earth by
pulling the earth away from the water, leaving
the latter of more than ordinary depth. The
sun is so much further off than the moon that
it eXerts smaller influence, notwithstanding
its immensely superior weight When the
moon and the sun attract in the same or OPP
poste directions the influence of both are the
same, and spring tides occur; when they are at
right angles, the sun partially counteracts the
moons attraction, and low tides are the con-
sequence. The above is the theory of the
tidal waves, and would be true in experience
with an ordinary tide of two or three feet if
the earth were wholly covered with water.
The irregular conformation of the land varies
the result much in different localities, causing
higher or lower tides, and in places retarding
their course many hours.