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A Swiss innovator in the study of the Earth's natural history.

Louis Agassiz

A Swiss innovator in the study of the Earth's natural history.

"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…

This illustration shows a perspective view and a vertical section of an anticline. It shows the half-cigar-shaped mountains of the hard rocks and the arches formed by the beds.

Anticline

This illustration shows a perspective view and a vertical section of an anticline. It shows the half-cigar-shaped…

"A tablet of dark brown clay, much injured, dating from the 8th or 7th century B.C. The two large concentric circles indicate the ocean, or, as it is called in the cuneiform writing between the circles, the 'Briny Flood.' Beyond the ocean are seven successive projections of land, represented by triangles. Perhaps they refer to the countries existing beyond the Black Sea and the Red Sea. The two parallel lines within the inner circle represent the Euphrates. The little rings stand for the Babylonian cities in this region."—Webster, 1913

A Babylonian Map of the World

"A tablet of dark brown clay, much injured, dating from the 8th or 7th century B.C. The two large concentric…

An illustration of a young boy looking at a globe.

Boy Looking at Globe

An illustration of a young boy looking at a globe.

Circle modeling the earth. O is the center of the earth, r the radius of the earth, and h the height of the point P above the surface; it is required to find the distance from the point P to the horizon at A.

Circle With Center o and Radius r with point P

Circle modeling the earth. O is the center of the earth, r the radius of the earth, and h the height…

A cliff is a slope perpendicular to a raised section of land.

Cliff

A cliff is a slope perpendicular to a raised section of land.

"Copernicus, or Nicholas Koppernigk, was the founder of modern astronomy. From a school in Thorn Copernicus went to Cracow, where he studied medicine, theology, mathematics, and astronomy. He latterly came to the following conclusions: That the sun was the center of the system; that the earth was a planet like Mars and Venus; and that all the planets revolve round the sun."—(Charles Leonard-Stuart, 1911)

Globe of Copernicus

"Copernicus, or Nicholas Koppernigk, was the founder of modern astronomy. From a school in Thorn Copernicus…

The Assumption and the Coronation of the Virgin is a woodcut created by Albrecht Dürer in 1510. It is part of a series called "Life of the Virgin". It depicts Mary being crowned by God and Jesus among the clouds. It shows heaven and earth, angels and mortals. A woodcut is created by carving an image on a wooden block and rolling ink over that surface and then printing it on paper.

The Assumption and the Coronation of the Virgin

The Assumption and the Coronation of the Virgin is a woodcut created by Albrecht Dürer in 1510.…

A Cuesta is a scarped ridge formed when one slope is steep and the other gentle, if one slope is a dip slope.

Cuesta

A Cuesta is a scarped ridge formed when one slope is steep and the other gentle, if one slope is a dip…

If the earth were flat, as soon as an object appeared on the horizon we would see the upper and lower parts at the same time; but if it were curved, the top parts would first be seen.

Curvature of the Earth's Surface

If the earth were flat, as soon as an object appeared on the horizon we would see the upper and lower…

"If we suppose a spectator placed at G, in the Earth's center, he would see the moon E, among the stars at I, whereas without changing the position of the moon, if that body is seen from A, on the surface of the Earth, it would appear among the stars at K. Now I is the true and K the apparent place of the moon, the space between them, being the Moon's parallax." —Comstock, 1850

Diurnal Parallax

"If we suppose a spectator placed at G, in the Earth's center, he would see the moon E, among the stars…

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the days and nights to differ at the same place at different seasons of the year, for on reviewing the positions of the globe at A, it will be observed that the line formed by the enlightened and dark hemispheres, does not coincide with the line of the axis and the pole, but that the line formed by the darkness and the light, extends obliquely across the line of the Earth's axis, so that the north pole is in the light while the south is in the dark. In the position A, therefore, an observer at the north pole would see the sun constantly, while another at the south pole would not see it at all. Hence those living in the north temperate zone, at the season of the year when the earth is at A, or in the Summer, would have long days and short nights, in proportion as they approached the polar circle; while those who live in the south temperate zone, at the same time, and when it would be Winter there, would have long nights and short days in the same proportion." —Comstock, 1850

Earth Axis

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the…

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the days and nights to differ at the same place at different seasons of the year, for on reviewing the positions of the globe at A, it will be observed that the line formed by the enlightened and dark hemispheres, does not coincide with the line of the axis and the pole, but that the line formed by the darkness and the light, extends obliquely across the line of the Earth's axis, so that the north pole is in the light while the south is in the dark. In the position A, therefore, an observer at the north pole would see the sun constantly, while another at the south pole would not see it at all. Hence those living in the north temperate zone, at the season of the year when the earth is at A, or in the Summer, would have long days and short nights, in proportion as they approached the polar circle; while those who live in the south temperate zone, at the same time, and when it would be Winter there, would have long nights and short days in the same proportion." —Comstock, 1850

Earth Axis

"Now it is the inclination of the Earth's axis, as above described, which causes the lengths of the…

"The Earth, whose diameter is 7,912 miles, is represented by the globe, or sphere. The straight line passing through its center, and about which it turns, is called its axis, and the two extremities of the axis are the poles of the Earth, A being the north pole, and B the south pole. The line C D, crossing the axis, passes quite round the Earth, and divides it into two equal parts. This is called the equinoctial line, or the equator. That part of the Earth situated north of this line, is caled the northern hemisphere, and that part south of it, the southern hemisphere. The small circles E F and G H, surrounding or including the poles, are called the polar circles." —Comstock, 1850

Earth Divisions

"The Earth, whose diameter is 7,912 miles, is represented by the globe, or sphere. The straight line…

"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,…

"A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The heavy line indicates the inclination of the earth's axis as compared with the plane of its orbit, which is represented by the base." -Wiswell, 1913

Inclination of Earth's Axis

"A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The…

"When one is at sea, or standing on the sea-shore, the first part of a ship seen at a distance, is its mast. As the bessel advances, te mast rises higher and higher above the horizon, and finally the hull, and whole ship, become visible. Now, were the Earth's surface an exact plane, no such appearance would take place, for we should then see the hull long before the mast or rigging, because it is much the largest object." -Comstock 1850

Spheroidal Form of the Earth

"When one is at sea, or standing on the sea-shore, the first part of a ship seen at a distance, is its…

"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 bodies of these animals are of a cylindrical form, somewhat pointed at the anterior extremity, and usually a little flattened at the tail. The skin is tough, and divided into numerous segments by transverse wrinkles, and the organs of motion are reduced to the form of a double row of bristles, running down the lower surface of the body." — Goodrich, 1859

Earth-worms

"The bodies of these animals are of a cylindrical form, somewhat pointed at the anterior extremity,…

"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." —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)…

An illustration of a globe (El mundo).

Globe

An illustration of a globe (El mundo).

"An artificial sphere on whose surface is drawn a map or representation of the earth." -Whitney, 1911

Terrestrial Globe

"An artificial sphere on whose surface is drawn a map or representation of the earth." -Whitney, 1911

A Great Circle is one which would be formed on the earth's surface by a plane passing through the earth's centre, hence dividing it into two equal parts. All great circles, therefore, divide the earth into two hemispheres.

Great Circle

A Great Circle is one which would be formed on the earth's surface by a plane passing through the earth's…

"The Gyroscope is an instrument constructed by M. Foucault to make the rotation of the earth visible. The principle on which it proceeds is this– that, unless gravity intervene, a rotating body will not alter the direction in which its permanent axis points. In the gyroscope there is a rotating metallic disk, the middle point of whose axis is also the center of gravity of the machine. By this device the action of gravity is eliminated."—(Charles Leonard-Stuart, 1911)

Gyroscope

"The Gyroscope is an instrument constructed by M. Foucault to make the rotation of the earth visible.…

A Hog's Back is a ridge where the crest is very rounded.

Hog's Back

A Hog's Back is a ridge where the crest is very rounded.

A Hollow is a land form where land falls on all sides to a minimum point.

Hollow

A Hollow is a land form where land falls on all sides to a minimum point.

Egyptian goddess of the Earth.

Isis

Egyptian goddess of the Earth.

"The magnetic poles of the earth do notc oincide with its geographical poles and, condequently, in some places, the magnetic needle does not point ot the geographical north. The angle that the axis of a compass-bneedle makes with the geographical meridian at any place is called the declination or variation of the needle at that place...Lines drawn through places on the earth where the declination is the sam are called isogonic lines, as shown." -Avery 1895

Isogonic Lines of Earth

"The magnetic poles of the earth do notc oincide with its geographical poles and, condequently, in some…

This specification discloses a land leveler comprising a massive rectangular frame including reinforced side bars and three crossbars that engage the ground surface for leveling purposes.

Land Leveler

This specification discloses a land leveler comprising a massive rectangular frame including reinforced…

"D is a Leyden jar, fastened to a stand in such a way that its outer armature can be insulated or connected to earth at will. The inner armature is in good metallic connection with the knob C. A horizontal metal piece A is mounted on a glass pillar, and carries another knob, which can be set at any required distance from C by means of a screw and graduation. The piece A is connected with the outer armature of the jar by a thin wire B contained in a glass tube." — Encyclopedia Britannica, 1893

Lanes Jar

"D is a Leyden jar, fastened to a stand in such a way that its outer armature can be insulated or connected…

"Let this figure represent the Earth, N being the north pole, S the south pole, and E W the equator. The lines 10, 20, 30, and so on, are the parallels of latitude, and the lines N a S, N b S, etc., are meridian lines, or those of longitude." —Comstock, 1850

Longitude

"Let this figure represent the Earth, N being the north pole, S the south pole, and E W the equator.…

The Meridian of any given place is that half of the meridian circle which passes through that place and both poles. A meridian of any place reaches from that place to both poles, and therefore is equal to one-half of a great circle, and, with the meridian directly opposite to it, forms a great circle called a meridian circle. There are as many meridians as there are places on the equator or on any parallel. Parallels are small circles which pass around the earth parallel to the equator.

Meridians and Parallels

The Meridian of any given place is that half of the meridian circle which passes through that place…

"When the Moon falls into the shadow of the Earth, the rays of the Sun are intercepted, or hid from her, and she then becomes eclipsed. when the Earth's shadow covers a part of her face, as seen by us, she suffers only a partial eclipse, one part of her disc being obscured, while the other part reflects the Sun's light. But when her whole surface is obscured by the Earth's shadow, she then suffers a total eclipse, and of a duration proportionate to the distance she passes through the Earth's shadow." —Comstock, 1850

Moon Eclipse

"When the Moon falls into the shadow of the Earth, the rays of the Sun are intercepted, or hid from…

"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." —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 elevation of the tides at c and d is produced by the causes already explained; but their elevation is not so great as normal, since the influence of the Sun acting in the direction a b, tends to counteract the Moon's attractive influence. These small tides are called neap tides, and happen only when the Moon is in her quadartures." —Comstock, 1850

Neap Tides

"The elevation of the tides at c and d is produced by the causes already explained; but their elevation…

"Two stars in the Big Dipper opposite the handle indicate the direction toward the North Star, which, though not very bright, is the first very noticeable star in line." -Wiswell, 1913

Finding the North Star

"Two stars in the Big Dipper opposite the handle indicate the direction toward the North Star, which,…

Diagram showing the circulation in an ideal ocean extending from pole to pole and covering one fourth the circumference of the earth.

Ideal Ocean Circulation

Diagram showing the circulation in an ideal ocean extending from pole to pole and covering one fourth…

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

Orbits

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

"One day in paradise is worth a thousand years on earth." -Trowbridge, 1866

Paradise Rebus

"One day in paradise is worth a thousand years on earth." -Trowbridge, 1866

"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." —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." —Comstock, 1850

Planet Motion

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

"Elliptical Orbits.—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." —Comstock, 1850

Planet Motion

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

"The motion of Saturn, Jupiter, and Mars with respect to Earth." — Encyclopedia Britanica, 1893

Planet Rotations

"The motion of Saturn, Jupiter, and Mars with respect to Earth." — Encyclopedia Britanica, 1893

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

Planet Sizes

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

The daughter of Caelus and Terra, or Heaven and Earth; the wife of Saturn, and mother of Jupiter, Juno, Ceres, Vesta, and several other deities.

Rhea

The daughter of Caelus and Terra, or Heaven and Earth; the wife of Saturn, and mother of Jupiter, Juno,…

The daughter of Caelus and Terra, or Heaven and Earth; the wife of Saturn, and mother of Jupiter, Juno, Ceres, Vesta, and several other deities.

Rhea

The daughter of Caelus and Terra, or Heaven and Earth; the wife of Saturn, and mother of Jupiter, Juno,…

"An apparatus drawn by oxen or horses, and used for scraping the earth in making or repairing roads, digging cellars, canals, etc. and generally for raising and removing loosened soil, etc. In use the scraper is held with the handles slightly elevated till it scoops up its charge of earth, which is held by the sides and back." —Whitney, 1889

Scraper, Meant to be Drawn by Oxen or Horses

"An apparatus drawn by oxen or horses, and used for scraping the earth in making or repairing roads,…

"Suppose the Earth to be in her Summer solstice, which takes place on the 21st of June. At this period she will be at a, having her north pole, n, so inclined towards the Sun, that the whole arctic circle will be illuminated, and consequently the Sun's rays will extend 23.25 degrees, the breadth of the polar circle, beyond the north pole." —Comstock, 1850

Seasons

"Suppose the Earth to be in her Summer solstice, which takes place on the 21st of June. At this period…

"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…

A small circle is one formed by a plane which does not cut the earth into two equal parts. The small circles are the <em>parallels</em>.

Small Circle

A small circle is one formed by a plane which does not cut the earth into two equal parts. The small…

"A crumb of soil (magnified). The white spaces represent air."&mdash;Finley, 1917

Crumb of soil

"A crumb of soil (magnified). The white spaces represent air."—Finley, 1917

"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…

"When the moon psses between the Earth and Sun, there happens an eclipse of the Sun, because then the Moon's shadow falls upon the Earth. A total eclipse of the Sun happens often, but when it occurs, the total obscurity is confined to a small part of the Earth; since the dark portion of the Moon's shadow never exceeds 200 miles in diameter on the Earth. But the Moon's partial shadow, or penumbra, may cover a space on the Earth of more than 4,000 miles in diameter, within all which space the Sun will be more or less eclipsed. When the penumbra first touches the Earth, the eclipse begins at that place, and ends when the penumbra leaves it. But the eclipse will be total only where the dark shadow of the Moon touches the earth." &mdash;Comstock, 1850

Sun Eclipse

"When the moon psses between the Earth and Sun, there happens an eclipse of the Sun, because then the…

"Let m be the Moon, and E the Earth covered with water. As the Moon passes round the Earth, its solid and fluid parts are equally attracted by her influence according to their densities; but while the solid parts are at liberty to move only as a whole, the water obeys the slightest impulse, and thus tends towards the Moon where her attraction is the strongest. Consequently, the waters are perpetually elevated immediately under the Moon. If, therefore, the Earth stood still, the influence of the Moon's attraction would raise the tides only as she passed round the Earth. But as the Earth turns on her axis every 24 hours, and as the waters nearest the Moon, as at a, are constantly elevated, they will, in the course of 24 hours, move round the whole Earth, and consequently from this cause there will be high water at every place once in 24 hours." &mdash;Comstock, 1850

Tides

"Let m be the Moon, and E the Earth covered with water. As the Moon passes round the Earth, its solid…

"Umbra and Penumbra. A solar eclipse, with the penumbra, d, c, and the umbra or dark shadow is seen here. When the Moon is at its greatest distance from the Earth, its shadow m o, sometimes terminates, before it reaches the Earth, and then an observer standing directly under the point o, will see the outer edge of the Sun, forming a bright ring around the circumference of the Moon, thus forming an annular eclipse." &mdash;Comstock, 1850

Umbra

"Umbra and Penumbra. A solar eclipse, with the penumbra, d, c, and the umbra or dark shadow is seen…

If land falls to a minimum line with a steady slope, the land form created is called a valley.

Valley

If land falls to a minimum line with a steady slope, the land form created is called a valley.

"The twelve signs of the zodiac, together with the Sun, and the Earth revolving around him. When the Earth is at A, the Sun will appear to be just entering the sign Aries, because then, when seen from the Earth, he ranges towards certain stars at the beginning of that constellation. When the Earth is at C, the Sun will appear in the opposite part of the heavens, and therefore in the beginning of Libra. The middle line, dividing the circle of the zodiac into equal parts, is the line of the ecliptic." &mdash;Comstock, 1850

Zodiac Signs

"The twelve signs of the zodiac, together with the Sun, and the Earth revolving around him. When the…