Browse Items (54 total)

The three prisms hanging from the brass stand may be folded up in pairs to demonstrate achromatism (no color separation) or constant deviation (no color dependence of the angle of minimum bending of light.) These were made by Lerebours et Secretan of…

A five decade variable resistor made by Max Kohl of Chemnitz. The 0.1 and 1 ohm resistors are slide wires along the front and back of the top, and the three upper ranges use coils of low-temperature coefficient resistance wire (probably constantan).…

In 1844 Froment devised an electric motor that was one of the first used for industrial purposes. In his design, electromagnets are energized to attract iron bars mounted on a revolving cage. Once the iron bar is level with the electromagnet, the…

This was a popular piece of demonstration apparatus, in which the operation of the motor is signaled by a ringing of the bell. The instrument is an inverted revolving electromagnet, with a gearing system added to strike the bell every hundred…

The tangent galvanometer is a current measuring device. It was first described in an 1837 paper by Claude-Servais-Mathias Pouillet (1790-1868), who later employed this sensitive form of galvanometer to verify Ohm's law. To use the galvanometer, it is…

The telegraph was invented by the artist and scientist Samuel Finley Breese Morse (1791-1872), who conceived the idea of the printing telegraph during an ocean voyage to Europe in 1832. The actuation of an electromagnet in the receiver would cause a…

The Magdeburg hemispheres are a pair of large copper hemispheres with mating rims. When the rims were sealed with grease and the air was pumped out through the valve below the lower hemisphere, the lowered pressure within the sphere made it very…

This is a demonstration device showing two aspects of electric charge. When the conducting sphere atop the vertical stand is charged (e.g. by using a Leyden jar) the horizontal pinwheel device at the top begins to spin as charge is leaked from its…

The Leyden jar is the earliest form of the condenser or capacitor. The jar allowed the electric charge produced by an electrostatic machine (for instance) to be accumulated and stored for future use. The first jars were made independently in 1745 by…

The basic discharger is simply a conductor used to discharge a Leiden jar. The two arms are spread apart at the hinged joint, and the insulated handle prevents the operator from receiving a shock as the knobs are touched against the outer foil and…