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"GEMELS. This word signifies double. The example contains two double bars, which in heraldic language would be called two bars gemels." -Hall, 1862

Bars Gemels

"GEMELS. This word signifies double. The example contains two double bars, which in heraldic language…

An illustration of a double buggy. Referred to as a double buggy because the buggy has two separate seats.

Double Buggy

An illustration of a double buggy. Referred to as a double buggy because the buggy has two separate…

"A medium-capacity, double-pole circuit breaker (250 volts, 200 amp. General Electric Company, type C, form G)." —Croft 1920

Circuit Breaker

"A medium-capacity, double-pole circuit breaker (250 volts, 200 amp. General Electric Company, type…

"The knife is a double-edged rectangular blade, about 12 inches by 5 inches, with a straight handle at one end, and a cross handle at the other in the plane of the blade." —The Encyclopedia Britannica, 1910

Currying Knife

"The knife is a double-edged rectangular blade, about 12 inches by 5 inches, with a straight handle…

"Old English double curtail (before 1688)." — The Encyclopedia Britannica, 1910

Curtail

"Old English double curtail (before 1688)." — The Encyclopedia Britannica, 1910

Illustration of 2 right circular cylinders in which one cylinder is twice the height of the other.

2 Right Circular Cylinders

Illustration of 2 right circular cylinders in which one cylinder is twice the height of the other.

Illustration of 2 right circular cylinders in which one cylinder is twice the height and twice the diameter of the other.

2 Right Circular Cylinders

Illustration of 2 right circular cylinders in which one cylinder is twice the height and twice the diameter…

An illustration of a double variety dahlia flower. Dahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There at least 36 species of Dahlia. Dahlia hybrids are commonly grown as garden plants. The Aztecs gathered and cultivated the dahlia for food, ceremony, as well as decorative purposes, and the long woody stem of one variety was used for small pipes

Dahlia

An illustration of a double variety dahlia flower. Dahlia is a genus of bushy, tuberous, perennial plants…

An illustration of a double border.

Double Border

An illustration of a double border.

"Usually kept as a family seat, and occupied by the master and mistress of the house, though occaisionally offered, as a special honor, to the guests." — Goodrich, 1844

Egyptian Double Chair

"Usually kept as a family seat, and occupied by the master and mistress of the house, though occaisionally…

"Probably the precursor of the Oar, and still is substitute among barbarous nations, is a wooden implement, consisting of a wide flat blade with a short handle, by means of which the operator spoons the water towards him." — Chambers, 1881

Double Paddle

"Probably the precursor of the Oar, and still is substitute among barbarous nations, is a wooden implement,…

"Double Strop -- Made with one piece of rope, the splice being brought as usual to the crown of the block t, the bights fitting into scores with some inches apart, converging to the upper part, above which the thimble receives the bights, a,a; and the four parts of the strop are secured at s, s, by a round seizing double crossed." -Britanncia, 1910

Double Strop

"Double Strop -- Made with one piece of rope, the splice being brought as usual to the crown of the…

Double threaded screw.

Double Threaded Screw

Double threaded screw.

"Two wedges have been placed toward one another underneath the weight. Equal force is applied to each wedge which raises the weight." —Quackenbos 1859

Double Wedge

"Two wedges have been placed toward one another underneath the weight. Equal force is applied to each…

"The first alteration to be noticed in the double-acting engine is that of the cylinder. To insure its double action, it is necessary to provide, at each end of the cylinder, a means of admission of steam from the boiler, and of escape for the steam to the condenser. Hence the double action, which means that the piston is both raised and depressed by the force of steam. For this purpose, a steam box is fixed to each end of the cylinder, communicating, in the one case with the upper, in the other with the lower, surface of the piston. B is the upper, and and B' the lower, steam box. Each of these boxes is furnished with two valves." —Comstock, 1850

Double-acting Cylinder

"The first alteration to be noticed in the double-acting engine is that of the cylinder. To insure its…

"The first alteration to be noticed in the double-acting engine is that of the cylinder. To insure its double action, it is necessary to provide, at each end of the cylinder, a means of admission of steam from the boiler, and of escape for the steam to the condenser. Hence the double action, which means that the piston is both raised and depressed by the force of steam. For this purpose, a steam box is fixed to each end of the cylinder, communicating, in the one case with the upper, in the other with the lower, surface of the piston. B is the upper, and and B' the lower, steam box. Each of these boxes is furnished with two valves." —Comstock, 1850

Double-acting Cylinder

"The first alteration to be noticed in the double-acting engine is that of the cylinder. To insure its…

"The softening of leather is helped and rendered thorough by working them for some time in the stocks after they have been well soaked." —The Encyclopedia Britannica, 1910

Double-Acting Stock

"The softening of leather is helped and rendered thorough by working them for some time in the stocks…

"A transverse section through the valve casing of a double-column hammer, used for heavy forge work."—Finley, 1917

Transverse Section of a Double-Column Hammer

"A transverse section through the valve casing of a double-column hammer, used for heavy forge work."—Finley,…

"A section through the valve casing of a double-column hammer, fitted with a valve v provided with three pistons."—Finley, 1917

Valve Casing of a Double-column Hammer

"A section through the valve casing of a double-column hammer, fitted with a valve v provided with three…

"A vertical section through the valve casing of a double-column hammer, used for heavy forge work."—Finley, 1917

Vertical Section of a Double-Hammer Column

"A vertical section through the valve casing of a double-column hammer, used for heavy forge work."—Finley,…

"The telephone standard and compound forms of Fuller cell... The Fuller cell is of the double fluid cariety and has the advantage over the Grenet type, in that the zinc is always kept well amalgamated and does not require removal from the solution." -Hawkins, 1917

Fuller Cell

"The telephone standard and compound forms of Fuller cell... The Fuller cell is of the double fluid…

Section of Hall double headlight.

Headlight

Section of Hall double headlight.

"A lens is a transparent body the two refracting surfaces of which are curved, or one of which is curved and the other plane.(1) Double convex(2) Plano convex(3) Meniscus(4)Double concave(5) Plano concave(6) Concavo concave." -Avery 1895

Lens

"A lens is a transparent body the two refracting surfaces of which are curved, or one of which is curved…

"A double convex lens of crown-glass may be combined with a plano-convex lens of flint-glass so as to overcome the dispersive effect for some of the colors without overcoming the converging effect." -Avery 1895

Achromatic Lens

"A double convex lens of crown-glass may be combined with a plano-convex lens of flint-glass so as to…

"The shape of the double convex lens, d, c, is that of two plano-convex lenses, placed with their plane surfaces in contact, and consequently the focal distance of this lens is nearly the centre of the sphere of which one of its surfaces is a part." -Comstock 1850

Double Convex Lens

"The shape of the double convex lens, d, c, is that of two plano-convex lenses, placed with their plane…

"Double convex lenses are used in the eyeglasses for old people, becoming more spherical according to the age of the person or the magnifing power required." -Comstock 1850

Double Convex Lens Magnifing an Arrow

"Double convex lenses are used in the eyeglasses for old people, becoming more spherical according to…

"The double convex lens may be described as the part common to two spheres that intersect each other. The centers of the limiting spherical surfaces, as c and C, are the centers of curvature. The straight line, XY, passing through the centers of curvature is the principal axis of the lens." -Avery 1895

Double Convex Lens

"The double convex lens may be described as the part common to two spheres that intersect each other.…

"Thus the pencils of converging rays, are rendered still more convergent by their passage through the lens, and are therefore brought to a focus nearer the lens, in proportion to their previous convergency." -Comstock 1850

Converging Rays and a Double Convex Lens

"Thus the pencils of converging rays, are rendered still more convergent by their passage through the…

"If diverging rays fall on the surface of the same lens, they will, by refraction, be rendered less divergent, parallel, or convergent, according to the degrees of their divergency, and the convexity of the surface of the lens." -Comstock 1850

Diverging Rays from a Double Convex Lens

"If diverging rays fall on the surface of the same lens, they will, by refraction, be rendered less…

The double-row marker, used for marking off the rows where seed or plants are to be planted.

Double-Row Marker

The double-row marker, used for marking off the rows where seed or plants are to be planted.

"This consists of two lenses, one of which is called the condesner, because it is employed to concentrate the rays of the sun...The other is a double convex lens, of considerable magnifing power, by which the image is magnified." -Comstock 1850

Solar Microscope

"This consists of two lenses, one of which is called the condesner, because it is employed to concentrate…

"Probably the precursor of the Oar, and still is substitute among barbarous nations, is a wooden implement, consisting of a wide flat blade with a short handle, by means of which the operator spoons the water towards him." — Chambers, 1881

Paddle

"Probably the precursor of the Oar, and still is substitute among barbarous nations, is a wooden implement,…

A double-wheeled hand plow.

Hand plow

A double-wheeled hand plow.

"Double cylinder press, 1835-1900. These presses were built up to 1900 and this picture shows the latest design brought out about 1882." -Hill, 1921

Double Cylinder Press

"Double cylinder press, 1835-1900. These presses were built up to 1900 and this picture shows the latest…

Illustration of 2 right octagonal prisms with congruent bases, but different heights. The height of the smaller prism is one half that of the larger.

2 Octagonal Prisms

Illustration of 2 right octagonal prisms with congruent bases, but different heights. The height of…

Illustration of 2 right rectangular prisms. The bases are congruent, but the height of the smaller prism is one half that of the larger. Hidden edges are shown.

2 Rectangular Prisms

Illustration of 2 right rectangular prisms. The bases are congruent, but the height of the smaller prism…

Illustration of 2 right rectangular prisms. The bases are congruent, but the height of the smaller prism is one half that of the larger.

2 Rectangular Prisms

Illustration of 2 right rectangular prisms. The bases are congruent, but the height of the smaller prism…

Illustration of 2 Similar right octagonal prisms. The height and length of the edges of the smaller prism are one half that of the larger.

2 Similar Octagonal Prisms

Illustration of 2 Similar right octagonal prisms. The height and length of the edges of the smaller…

Illustration of 2 similar right decagonal prisms. Both have regular decagons for bases and rectangular faces. The height of the prism and length of the side of the decagon on the smaller decagonal prism are one half that of the larger.

Similar Decagonal Prisms

Illustration of 2 similar right decagonal prisms. Both have regular decagons for bases and rectangular…

Illustration of 2 similar right heptagonal/septagonal prisms. Both have regular heptagons/septagons for bases and rectangular faces. The height of the prism and length of the side of the heptagon on the smaller heptagonal prism are one half that of the larger.

Similar Heptagonal/Septagonal Prisms

Illustration of 2 similar right heptagonal/septagonal prisms. Both have regular heptagons/septagons…

Illustration of 2 similar right hexagonal prisms. The height of the prism and length of the side of the hexagon on the smaller hexagonal prism are one half that of the larger.

Similar Hexagonal Prisms

Illustration of 2 similar right hexagonal prisms. The height of the prism and length of the side of…

Illustration of 2 similar right hexagonal prisms. The height of the prism and length of the side of the hexagon on the smaller hexagonal prism are one half that of the larger.

Similar Hexagonal Prisms

Illustration of 2 similar right hexagonal prisms. The height of the prism and length of the side of…

"A double-acting pump of the piston pattern is shown [here]. Such a pump has two sets of suction valves and delivery valves, one set for each side of the piston. With the piston moving in the direction of the arrow, the pressure of the atmosphere forces the water up the suction pipe P into the left-hand end of the pump cylinder, the left-hand suction valve opens and the left-hand delivery valve is closed...The water now flows up the delivery pipe P'." —Hallock 1905

Double-acting Force Pump

"A double-acting pump of the piston pattern is shown [here]. Such a pump has two sets of suction valves…

Illustration of 2 right pentagonal pyramids with hidden edges shown. The pentagonal bases are congruent, but the height of the smaller pyramid is one half that of the larger.

2 Right Pentagonal Pyramids

Illustration of 2 right pentagonal pyramids with hidden edges shown. The pentagonal bases are congruent,…

Illustration of 2 right rectangular pyramids with hidden edges shown. The rectangular bases are congruent, but the height of the smaller pyramid is one half that of the larger.

2 Right Rectangular Pyramids

Illustration of 2 right rectangular pyramids with hidden edges shown. The rectangular bases are congruent,…

Illustration of 2 similar right pentagonal pyramids with hidden edges shown. The height of the pyramid and length of the side of the pentagon (base) on the smaller pentagonal pyramid are one half that of the larger.

Similar Pentagonal Pyramids

Illustration of 2 similar right pentagonal pyramids with hidden edges shown. The height of the pyramid…

"Fill with carbon dioxide a large rubber toy balloon or other double-convex lens having easily flexible walls. Suspend a watch, and place yourself so that you can just hear its ticking. Have the gas-filled lens moved back and forth in the line between watch and and ear until the ticking is much more plainly heard. Use a glass funnel as an ear-trumpet." -Avery 1895

Sound Refraction

"Fill with carbon dioxide a large rubber toy balloon or other double-convex lens having easily flexible…

"In marching in double time the saber is carried diagonally across the breast, edge to the front; the left hand steadies the scabbard." — Moss, 1914

Marching with Saber

"In marching in double time the saber is carried diagonally across the breast, edge to the front; the…

In military affairs, a narrow ditch or trench by which approach is made to a fortress or designed place when within range of fire. This is a double sap on the serpentine plan.

Double Sap

In military affairs, a narrow ditch or trench by which approach is made to a fortress or designed place…

"A self-acting screw-cutting lathe with double-geared headstock, of a type now well established, the arrangements for obtaining and varying this traversing motion may be observed. A steel leading screw runs along the front of the lathe bed, and with it the slide rest can be connected at pleasure. Two or more change wheels, properly proportioned as to the number of their teeth, connect the head of the screw with the hinder end of the mandrel." —The Encyclopedia Britannica, 1903

Screw-Cutting

"A self-acting screw-cutting lathe with double-geared headstock, of a type now well established, the…

"...shows a piece in double shear; here the central piece c d is forced out, while the ends remain on their supports M and N." —Hallock 1905

Double Shear

"...shows a piece in double shear; here the central piece c d is forced out, while the ends remain on…

The double snipe, also known as the solitary snipe and the great snipe, is found sparingly throughout Europe.

Double Snipe

The double snipe, also known as the solitary snipe and the great snipe, is found sparingly throughout…

"The inversion of the object is of little consequence when the instrument is employed for astronomical purposes, for since the forms of the heavenly bodies are spherical, their positions, in this respect, do not affect their general appearance. But for terrestrial purposes, this is manifestly a great defect, and therefore those constructed for such purposes, as ship, or spyglasses, have two additional lenses, by means of which, the images are made to appear in the same position as the objects. These are called double telescopes." -Comstock 1850

Double Refracting Telescope

"The inversion of the object is of little consequence when the instrument is employed for astronomical…

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having a long, and the other a short, focal distance." -Comstock 1850

Refracting Telescope

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having…

Dual Blank Lab Thermometer

Dual Lab Celsius Centigrade Thermometers

Dual Blank Lab Thermometer

Dual Lab Thermometers 0 Degrees Celsius Centigrade

Dual Lab Celsius Centigrade Thermometers

Dual Lab Thermometers 0 Degrees Celsius Centigrade

Dual Lab Thermometers -5 Degrees Celsius Centigrade

Dual Lab Celsius Centigrade Thermometers

Dual Lab Thermometers -5 Degrees Celsius Centigrade

Dual Lab Thermometers -10 Degrees Celsius Centigrade

Dual Lab Celsius Centigrade Thermometers

Dual Lab Thermometers -10 Degrees Celsius Centigrade

Dual Lab Thermometers -15 Degrees Celsius Centigrade

Dual Lab Celsius Centigrade Thermometers

Dual Lab Thermometers -15 Degrees Celsius Centigrade

Dual Lab Thermometers -20 Degrees Celsius Centigrade

Dual Lab Celsius Centigrade Thermometers

Dual Lab Thermometers -20 Degrees Celsius Centigrade