Grinnell College Physics Museum

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Homemade Galvanometer

When Frank Almy came to Grinnell College in 1893 to teach physics, laboratory equipment was not as readily available as it was later. Probably the cost of equipment also placed a severe constraint on purchases. Almy made a number of galvanometers, some of which survive. One of those galvanometers is shown here. It had a mirror attached to small magnets suspended between coils.

Epinius' Condenser

This is a capacitor with adjustable plates and a plate of glass which can be inserted between the plates. With static charges on the plates, the effects of plate separation and nature of the dielectric between the plates can be studied. This was purchased from Queen & Company, but the date is unknown.

McIntosh Milliammeter

One of these is in the Smithsonian labeled a “dosage meter.” It probably is part of a medical fake.

Eight Leyden Jars in a Box

The Leyden Jar was a sensational advancement for studies of electricity in the 18th century. A high voltage device made from simple materials, it was the first condenser, a precursor to the capacitor, storing electric energy until discharged. Such a device enabled a number of medical, engineering, and experimental applications. The Leyden Jar is a wide mouthed glass with metal wrapped around the outside and on the inside. The jar is filled with water or another liquid such as alcohol. A metal rod passes through the nonconductive top, reaching down to the liquid. When an electric charge is created (in this period, by an electrostatic friction machine) and somebody or a conductive object touches both the metal top of the rod and the outside metal, an electric shock jumps springs between the rod and the conductive agent, discharging the electricity stored in the jar's glass. Two parties are credited with its invention, independently but around the same time: Ewald Georg von Kleist and Pieter van Musschenbroek, in 1745-1746. Musschenbroek and his assistant, Andreas Cunaeus, are given the namesake as they published their findings. It is named for the town and the University of Leiden, where they worked. Beyond its scientific merit, it was promoted commercially as a 'flask' for wealthy people with scientific wonder. The Leyden jars at Grinnell College are arranged in a box configuration, an advancement made by Benjamin Franklin in 1747-1748. This setup creates the "Leyden Battery," allowing a stronger charge to be collectively built and stored. Such a design enabled the invention of the wireless telegraph at the beginning of the 20th century. -Felipe Gentle 2017 References Katz, Eugenii. "Pieter (Petrus) Van Musschenbroek." Musschenbroek. Institute of Chemistry, Hebrew University of Jerusalem, 2004. Web. 12 Apr. 2017. Terra Incognita Interactive Productions. "'Electrical Battery' of Leyden Jars, 1760-1769." The Benjamin Franklin Tercentenary. Franklin and Marshall College, n.d. Web. 12 Apr. 2017. Wikisource contributors. "1911 Encyclopædia Britannica/Leyden Jar." Wikisource . Wikisource , 8 Sep. 2016. Web. 13 Apr. 2017. _________________________________________ A Leyden jar is a device made from a glass jar coated inside and out with metal sheets and a conducting rod inserted vertically through the jar to make contact with both the inner and outer sheets. The Leyden jar was the first form of a capacitor or condenser—a circuit device which stores electrical charge. It was independently designed by both the German deacon Ewald Georg von Kleist in 1744 and the Dutch scientists Pieter van Musschenbroek and Andreas Cunaeus in 1746 at the University of Leyden—hence its name. The development of the Leyden jar derives from an early conception of electricity as a fluid, wherein electricity was thought to be storable in containers using water or alcohol. Early attempts at storing electricity featured the conduction of electricity into a water-filled jar and discharging this electricity to the ground through a human interface. Successfully development allowed charging of the jar through the connection of one terminal of an electrostatic generator to the conducting rod and one to the outer foil. After charging, Leyden jars proved to be useful as portable sources of current through which experiments and demonstrations could be carried out, possibly in contexts where the use of an electrostatic generator is inconvenient and/or impossible. These particular Leyden jars are connected in parallel which allows for the storage of greater charge than an individual jar. This parallel connection was pioneered by Benjamin Franklin, who’s study of Leyden jars—and electricity in general—helped contribute the “drastic revision of the [electricity] fluid theory. . . and the first full paradigm for electricity” (Kuhn, The Structure of Scientific Revolutions, p. 62). -Ben Hoekstra 2019

AC Ammeter

0-15 Amperes Pattern 11

DC Voltmeter with Case

0-150 Volts DC

Potentiometer

Serial No. 26686

Voltmeter 420

0-10 Volts DC Model 420