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"The balance is essentially a lever of the first class, having equal arms. The beam carries a pan at each end, one for the weidhts used, the other for the article to be weighed." -Avery 1895

Balance

"The balance is essentially a lever of the first class, having equal arms. The beam carries a pan at…

A cat sneaking up on a mouse teaching a class how to escape from cats.

Cat and Mice

A cat sneaking up on a mouse teaching a class how to escape from cats.

"The common chipping-knife, used by apothecaries, and represented [here], is a familiar illustration of levers of the second kind [class]." —Quackenbos 1859

Chipping Knife

"The common chipping-knife, used by apothecaries, and represented [here], is a familiar illustration…

"An outdoor classroom at Williamsburg, Virginia. When the children becoem tired indoors, classes are taken to this building for a recitation. There were only 20 days during the winter of 1911-1912 on which this outdor classroom was not used." — Ritchie, 1918

Outdoor classroom

"An outdoor classroom at Williamsburg, Virginia. When the children becoem tired indoors, classes are…

"... shows one of the commonest (sic) forms in which this kind of lever appears,-the crowbar. The power is applied at the handle. The weight is at the other end, and consists of something to be moved. The fulcrum is a stone on which the crowbar rests." —Quackenbos 1859

Crowbar

"... shows one of the commonest (sic) forms in which this kind of lever appears,-the crowbar. The power…

A lever of the first class

First Class Lever

A lever of the first class

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the fulcrum is between the power and weight, the lever is of the first class." — Avery, 1895

First Class Lever

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the fulcrum is…

"First class lever." -Comstock 1850

First class lever

"First class lever." -Comstock 1850

"First class lever." -Comstock 1850

First-class Lever

"First class lever." -Comstock 1850

"In straight levers of the first kind, the fulcrum is between the power and the resistance, as in fig 1, where F is the fulcrum of the lever AB; P is the power, and W the weight or resistance."—Pettigrew, 1874

First Kind of Lever

"In straight levers of the first kind, the fulcrum is between the power and the resistance, as in fig…

"In the second order of levers, the resistance is between the fulcrum and the power; and, as before, P : W :: BF : AF, but the pressure of the fulcrum is equal to W-P, or the weight less the power."—Pettigrew, 1874

Second Kind of Lever

"In the second order of levers, the resistance is between the fulcrum and the power; and, as before,…

"In the third order of lever the power acts between the prop and the resistance, where also P : W :: BF : AF, and the pressure on the fulcrum is P-W, or the power less the weight."——Pettigrew, 1874

Third Kind of Lever

"In the third order of lever the power acts between the prop and the resistance, where also P : W ::…

Mygale fodiens, part of the Arachnidia class.

Mygale Fodiens

Mygale fodiens, part of the Arachnidia class.

"The symmetry of the Normal Class of the Hexagonal System is as follows: The vertical crystallographic axis is an axis of hexagonal symmetry. There are six horizontal axes of binary symmetry, three of them being coincident with the crystallographic axes and the other three lying midway between them." — Ford, 1912

Symmetry of normal class

"The symmetry of the Normal Class of the Hexagonal System is as follows: The vertical crystallographic…

"The vertical crystallographic axis is one of trigonal symmetry, and the three horizontal crystallographic axes of binary symmetry." — Ford, 1912

Symmetry of Rhombohedral Class

"The vertical crystallographic axis is one of trigonal symmetry, and the three horizontal crystallographic…

An illustration of a Pompeiian wall painting of school materials, including scrolls, books, writing utensils, coins, and purses. The illustration is divided into six sections.

Roman School Materials - Based on a Wall Painting from Pompeii

An illustration of a Pompeiian wall painting of school materials, including scrolls, books, writing…

"Sant Apollinare in Classe, at Ravenna." —D'Anvers, 1895

Sant Apollinare

"Sant Apollinare in Classe, at Ravenna." —D'Anvers, 1895

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the weight is between the power and the fulcrum, the lever is of the second class." — Avery, 1895

Second Class Lever

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the weight is…

"The second kind of lever is represented where W is the weight, L the lever, F the fulcrum, and P a pulley, over which a string is thrown, and a weight suspeneded, as the power." -Comstock 1850

Second-class Lever

"The second kind of lever is represented where W is the weight, L the lever, F the fulcrum, and P a…

"Two men carrying a load between them on a pole is also and example of this [second class] kind of lever. Each man acts as the power in moving the weight, and at the same time each becomes the fulcrum in respect to the other." -Comstock 1850

Second-class Lever

"Two men carrying a load between them on a pole is also and example of this [second class] kind of lever.…

"Second class lever." -Comstock 1850

Second-class lever

"Second class lever." -Comstock 1850

"A Lever of the Second Kind is one in which the weight is between the power and the fulcrum." —Quackenbos 1859

Second Class Lever

"A Lever of the Second Kind is one in which the weight is between the power and the fulcrum." —Quackenbos…

"The Sphenoidal Class corresponds in the Tetragonal system to the Tetrahedral class in the Isometric System. It is characterized by the following symmetry: The three crystallographic axes are axes of binary symmetry, and there are two vertical diagonal planes of symmetry." — Ford, 1912

Symmetry of Sphenoidal class

"The Sphenoidal Class corresponds in the Tetragonal system to the Tetrahedral class in the Isometric…

A teacher in front of her classroom.

Teacher

A teacher in front of her classroom.

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the power is between the weight and the fulcrum the lever is of the third class." — Avery, 1895

Third class lever

"A lever is an inflexible bar freely movable about a fixed axis called the fulcrum. If the power is…

"In the third and last kind of lever, the weight is placed at one end, the fulcrum at the other end and the power between them, or the hand s between the fulcrum and the weight." -Comstock 1850

Third-class Lever

"In the third and last kind of lever, the weight is placed at one end, the fulcrum at the other end…

"Third class lever." -Comstock 1850

Third Class Lever

"Third class lever." -Comstock 1850

"A Lever of the Third Kind is one in which the power is between the weight and the fulcrum." —Quackenbos 1859

Third Class Lever

"A Lever of the Third Kind is one in which the power is between the weight and the fulcrum." —Quackenbos…

"The wheel and axle consists of a wheel united to a cylinder in such a way that they may turn together on a common axis. It is a modified lever of the first or second class." -Avery 1895

Wheel and Axle with Rope and Bucket

"The wheel and axle consists of a wheel united to a cylinder in such a way that they may turn together…