Browse Items (54 total)

This late 19th century instrument is often called a Ruhmkorff coil, after the Parisan apparatus manufacturer Heinrich Daniel Ruhmkorff (1803-1877). Although he did not invent the induction coil, his name is often associated with it (particularly in…

The heliostat takes light from the sun as it tracks across the sky, and redirects it in a fixed direction. To accomplish this, the light is reflected from a mirror that reproduces the motion of the sun, except at twice the rate. Although he did not…

Glass, when stressed, shows the property of double refraction: light of differing polarization directions bends differently passing through the glass. When placed between crossed polarizers , bands of color may be seen, with the spacing of the bands…

NOT YET LOCATED. The term “galvanometer” is in current use, naming an instrument which indicates the strength of an electric current. The Galvanoscope is an earlier instrument, which shows the presence of the current but gives only a rough…

In the nineteenth century almost all power supplies were direct current (DC). In order to step voltage up or down, the direct current had to be converted to alternating current (AC), stepped using transformers, and then converted back to DC. The…

NOT YET LOCATED. When two wires made of different metals are connected to make a loop, and the two junctions between the wires are held at different temperatures, a voltage is produced and electrical current can be detected with a sensitive current…

A current balance measures the force of repulsion between two wires, each carrying an electric current. An upper wire is fixed in place, and the wire directly below it is free to move. The currents are adjusted so that the electrical attractive force…

This early relative of the slide rule has a cylinder 4 in. in diameter and 18 in. long that rotates and slides in and out between the array of twenty equally-spaced parallel bars. The bars have a scale with numbers spaced logarithmically, as on a…

This is a device used to demonstrate the effect of atmospheric pressure. A glass vessel with openings at the bottom and top has its large top opening covered by a piece of animal bladder that is tied to seal it around its edges. As air is pumped from…

Lightning is the ultimate arc lamp, and so Benjamin Franklin's 1752 experiment of drawing electricity from the clouds and jumping a spark is perhaps the first arc lamp. In 1801 Humphry Davy observed the brilliant spark obtained when the connection…