"Suppose a to be a stationary celestial object, then as the Earth makes her annual revolution around the Sun S, this object at one time will appear among the stars at e, but six months after, when the Earth comes to the opposite point in her orbit, the same object will be seen at c, the space from c to e being the annual parallax of the object a. But the distances of the stars are so great that the diameter of the Earth's orbit, or 190,000,000 of miles make no difference in their apparent places. Were the fixed stars within 19 trillions of miles, their distance could be told by their parallaxes." —Comstock, 1850

Annual Parallax

"Suppose a to be a stationary celestial object, then as the Earth makes her annual revolution around…

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during the first and last quarters, they are at right angles. The portions of the earth and moon turned toward the sun are illumined, the shaded portions are in the darkness. To an observer on the earth, the moon, at <em>a</em>, appears new, since the dark part is turned toward the person; at <em>b</em>, however, it must appear full, since the illumined portions are toward the person. At <em>c</em>, and <em>d</em>, the positions of the quarters, only one-half of the illumined half, or one quarter, is seen.

Cause of the Phases of the Moon

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during…

"The earth shown as it would be if its axis were perpendicular to the plane of the orbit." -Wiswell, 1913

Earth's Axis Perpendicular to Plane of Orbit

"The earth shown as it would be if its axis were perpendicular to the plane of the orbit." -Wiswell,…

"Were the Earth's orbit a perfect circle, and her axis perpendicular to the plane of this orbit, the days would be of a uniform length, and there would be no difference between the clock and the Sun." -Comstock 1850

Suns in the Equator and Ecliptic

"Were the Earth's orbit a perfect circle, and her axis perpendicular to the plane of this orbit, the…

"The elliptical circle being supposed to be the Earth's orbit, with the Sun, S, in one of the foci. Now the spaces, 1, 2, 3, etc., though of different shapes, are of the same dimensions, or contain the same quantity of surface. The Earth, we have already seen, in its journey round the Sun, describes an ellipse, and moves more rapidly in one part of its orbit than in another. But whatever may be its actual velocity, its comparative motion is through equal areas in equal times. Thus its center passes from E to C, and from C to A, in the same period of time, and so of all the other divisions marked in the figure." &mdash;Comstock, 1850

Elliptical Orbit

"The elliptical circle being supposed to be the Earth's orbit, with the Sun, S, in one of the foci.…

"Relative positions of the earth and the sun on March 21 (spring equinox) and September 21 (autumn equinox) as seen from the position occupied by the earth on June 21 (summer solstice). Rays of light and heat meet the earth vertically on the Equator, and the days and nights are everywhere of equal length." -Wiswell, 1913

Spring Equinox and Autumn Equinox

"Relative positions of the earth and the sun on March 21 (spring equinox) and September 21 (autumn equinox)…

Muscles of the right eye.

Muscles of the Eye

Muscles of the right eye.

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as at <em>a</em>, would cause the water to lose its globular form, become bulged at <em>a</em>, and <em>b</em>, and flattened at <em>c</em>, and <em>d</em>. In other words, the water would become <em>deeper</em> at <em>a</em>, and <em>b</em>, at the parts of the earth nearest and farthest from the moon and <em>shallower</em> in all places 90 degrees or at right angles to these points.

Lunar Tide

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as…

"Let S be the Sun, E the Earth, and A, B, C, D, F, the Moon in different parts of her orbit. Now when the Moon changes, or is in conjunction with the Sun, as at A, her dark side is turned towards the Earth, and she is invisible, as represented at a. The Sun always shines on one half of the Moon, in every direction, as represented at A and B, on the inner circle; but we at the Earth can see only such portions of the enlightened part as are turned towards us. After her change, when she has moved from A to B, a small part of her illuminated side comes in sight, and she appears horned, as at b, and is then called the new Moon. When she arrives at C, severel days afterwards, one half of her disc is visible, and she appears as at c, her appearance being the same in both circles. At this point she is said to be in her first quarter, because she has passed through a quarter of her orbit, and is 90 degrees from the place of her conjunction with the Sun. At D, she shows us still more of her enlightened side, and is then said to appear gibbous as at d. When she comes to F, her whole enlightened side is turned towards the Earth, and she appears in all the spendor of a full Moon." &mdash;Comstock, 1850

Moon Phases

"Let S be the Sun, E the Earth, and A, B, C, D, F, the Moon in different parts of her orbit. Now when…

The muscles of the orbit from above.

Orbital Muscles from Above

The muscles of the orbit from above.

The muscles of the orbit from without.

Orbital Muscles from Without

The muscles of the orbit from without.

Transverse vertical section through the orbit behind the eyeball to show the arrangement of muscles.

Arrangement of Orbital Muscles

Transverse vertical section through the orbit behind the eyeball to show the arrangement of muscles.

Schematic representation of the nerves which transverse the cavity of the orbit.

Orbital Nerves

Schematic representation of the nerves which transverse the cavity of the orbit.

"The orbits of Mars, Earth, Venus, and Mercury." &mdash; Encyclopedia Britanica, 1893

Orbits

"The orbits of Mars, Earth, Venus, and Mercury." — Encyclopedia Britanica, 1893

"Relative distance of the Planets. Having now given a short account of each planet composing the solar system, the relative situation of their several orbits, with the exception of those of the Asteroids, are shown in this figure. The orbits are marked by the signs of each planet, of which the first, or that nearest the Sun, is Mercury, the next Venus, the third the Earth, the fourth Mars then come those of the Asteroids, then Jupiter, then Saturn and lastly Herschel." &mdash;Comstock, 1850

Planet Distance

"Relative distance of the Planets. Having now given a short account of each planet composing the solar…

"Circular Motion of the Planets." &mdash;Comstock, 1850

Planet Motion

"Circular Motion of the Planets." —Comstock, 1850

"Elliptical Orbits.&mdash;It has been supposed that the Sun's attraction, which constitutes the Earth's gravity, was at all times equal, or that the Earth was at an equal distance from the Sun, in all parts of its orbit." &mdash;Comstock, 1850

Planet Motion

"Elliptical Orbits.—It has been supposed that the Sun's attraction, which constitutes the Earth's…

"The comparative dimensions of the planets." &mdash;Comstock, 1850

Planet Sizes

"The comparative dimensions of the planets." —Comstock, 1850

The flood tides are the highest, and the ebb tides are the lowest. These are called <em>spring tides</em>. They occur twice during every revolution of the moon-once at <em>full</em>, and once at <em>new</em> moon. When the sun and moon are 90 degrees apart, each produces a tide on the portion of the earth directly under it, diminishing somewhat produced by the other body. High tide, then, occurs under the moon, while the high tide caused by the sun, becomes by comparison, a low tide. Such tides are called <em>neap tides</em>.

Positions

The flood tides are the highest, and the ebb tides are the lowest. These are called spring tides.…

"Relative positions of the earth and the sun during the spring equinox, the summer solstice, the autumn equinox, and the winter solstice." -Wiswell, 1913

Seasons from Earth's Orbit

"Relative positions of the earth and the sun during the spring equinox, the summer solstice, the autumn…

"Relative positions of the earth and the sun on June 21, the summer solstice. Summer and long days north of the Equator; winter and short days south of it." -Wiswell, 1913

Summer Solstice

"Relative positions of the earth and the sun on June 21, the summer solstice. Summer and long days north…

"Relative positions of the earth and the sun on December 21, the winter solstice. Winter and short days north of the Equator; summer and long days south of it. 1, North Frigid Zone; 2, North Temperate Zone; 3, Torrid Zone; 4, South Temperate Zone; 5, South Frigid Zone." -Wiswell, 1913

Winter Solstice

"Relative positions of the earth and the sun on December 21, the winter solstice. Winter and short days…