|| Capacitors were used in the laboratory for measuring large
resistance by measuring the time constant of an RC combination, and were
also part of alternating current capacitance
This Standard Mica Condenser is listed in the Leeds and Northup Catalogue 10, "Capacitance, Inductance and Magnetic Measurements" from 1927 at $65. It was "subdivided into 5 sections: 0.5, 0.2, 0.2, 0.05, 0.05 microfarad. Connections engraved on hard rubber top plate. Accuracy, .25% for all sections. Mounted in polished mahogany case with cover." The use of knife switches obviated the use of easily-lost plugs, and the reduced mass of metal on the top plate reduced stray capacitances.
This apparatus is in the Greenslade Collection.