### Balance

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

### Cat and Mice

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

### Chipping Knife

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

### Outdoor classroom

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

### Crowbar

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

### First Class Lever

A lever of the first class

### 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

"First class lever." -Comstock 1850

### First-class Lever

"First class lever." -Comstock 1850

### First Kind of Lever

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

### Second Kind of Lever

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

### 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

Mygale fodiens, part of the Arachnidia class.

### Symmetry of normal class

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

### Symmetry of Rhombohedral Class

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

### 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

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

### Second Class Lever

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

### Second-class Lever

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

### 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

"Second class lever." -Comstock 1850

### Second Class Lever

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

### Symmetry of Sphenoidal class

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

### Teacher

A teacher in front of her classroom.

### Third class lever

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

### 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

"Third class lever." -Comstock 1850

### Third Class Lever

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

### 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…