Table of Contents:
- Thomas B. Greenslade on John Tyndall Although not a history of Wheatstone bridges, this paper illustrates the variety of these electrical devices in the 19th and 20th c as well as some of their common applications.
- Allan Mills on Micro and Reed Switches Many 20th c technical objects have required switches operating at high current but without allowing an arc as the action “snaps off-on or vice versa. This paper investigates the development of these switches in the US.
- Thomas B. Greenslade on Charles Grafton Page and His Shocking Coil Charles Grafton Page, M.D. was the first American to do extensive research based the new science of Magneto-Electricity. His 1838 Shocking Coil was one of the ancestors of the induction coil, and is one of the first practical applications of Faraday’s 1831 discovery of electromagnetic induction.
- Allan Mills on the Nernst Lamp ‘The Nernst Lamp’, is a little-known contemporary of the carbon filament lamp. Employing ceramic insulators with embedded oxides and heated with platinum coils, Nernst lamps were bright and did not require a vacuum. However, their cost could not later compete with tungsten coil lamps.
- Deborah Jean Warner on The Sprengnethers and their Seismographs St. Louis, MD father and son, William Francis Sprengnether, Sr. and Jr., developed a range of seismic and related instruments in the 20th c. The Sprengnethers had many contacts in the academic and scientific communities and their equipment became key elements in some nodes of the global seismic network.
- Allan Mills on Selenium and Light The element selenium is sensitive to light, varying both its electrical resistance and generating a small photovoltaic current proportional to the intensity of illumination falling upon it. The latter property was employed in the ‘Megatron’ cell for measuring the intensity of light in a range of situations. The cell is described here, together with other applications of selenium to monitoring light.
- Allan Mills on The Spherometer The spherometer is a simple instrument for determining the radius of curvature of convex or concave mirrors and lenses. The construction of two alternative forms is illustrated, and the associated calculation explained.
- Thomas B. Greenslade on Photometers Photometers are used to compare the intensity of one light source to another. If you know something about the properties of the standard light source, you now have a number that you can use to study illumination. The Photometers discussed in this paper depend on the perceived overall reaction of the human eye, which has a sensitivity that is both wavelength and intensity dependent.
- Thomas B. Greenslade on A Span of (Wheatstone) Bridges A collection of 15 bridges are illustrated.