Browse Items (341 total)

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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This apparatus is listed in the 1885 catalogue of Jules Duboscq of Paris as the “Grand Circle of MM. Jamin et Sénnarmont.” It was designed for the study of the laws of polarized light reflected from crystalline substances, from liquids and from…

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Friedrich Wilhelm Georg Kohlrausch (1840-1910) was a professor of physics at Göttingen, Zürich, Würtzburg, Strasbourg and Berlin during his career. He wrote a widely-used book on methods of experimental physics, and developed improved measurement…

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NOT YET LOCATED. The effects of electricity on the body can be traced back to 1745 when Pieter van Musschenbroek, testing out the one of the first Leiden jars, stated that "I felt myself struck in my arms, shoulders, and breast. I lost my breath, and…

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The label of this electric motor notes that it is a 1/6 HP, 130 Volt motor made by the Crocker Wheeler Motor Company of New York. The patent dates are May 5 and September 22, 1891.

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This device demonstrates “Newton’s Rings,” colorful interference fringes caused by a thin air layer first discussed by Isaac Newton in a communication to the Royal Society in December 1675, and presented an expanded account in his book "Optics"…

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NOT YET LOCATED. The description below is not for these exact items. It belongs to a very similar item, which might nonetheless be helpful to the viewer. This cardboard aid for astronomy students was published by Henry Whitall, 512 Arch Street,…

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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…

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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).…

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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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…

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When this device is connected between two points in a circuit, it measures the relative voltage between the points by passing current through a coil of many turns of fine wire which, in turn, causes the needle to deflect.  

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This was the culmination of over a century of development of current-measuring instruments which relied on the interaction of currents with static magnetic fields. These instruments were mounted on a solid wall to prevent vibration, and a telescope…

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When the large center disk, made of non-conducting material with metallic strips attached, was turned using a hand crank, fixed metallic brushes rubbed against the metallic strips causing them to become charged. The charge was drawn off and collected…

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Prisms have been standard laboratory equipment since Isaac Newton used one in 1666 to study the nature of the spectrum. Most or all of these prisms were made by Duboscq in Paris.

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A tachometer (revolution-counter, Tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue…

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Kaleidoscopes operate on the principle of multiple reflection, where several mirrors are attached together. There are three rectangular lengthwise mirrors. Setting the mirrors at a 45 degree angle creates eight duplicate images of the objects, six at…
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