Robert A. Chipman 



THE EARLIEST 



ELECTROMAGNETIC 



INSTRUMENTS 



The history of the early stages of electromagnetic instrumenta- 

 tion is traced here through the wen who devised the theories and 

 constructed the instruments. 



Despite the many uses nude of voltaic cells after Volta's 

 announcement of his "pile" invention in 1X00, two decades 

 passed before Oersted discovered the magnetic effects of a voltaic 

 circuit. As a result of this and within a five-month period, 

 three men, apparently independent/) , announced the invention of 

 the "first" electromagnetic instrument. This article details the 

 merits of their claims to priority. 



The Author: Robert A. Chipman is chairman of the De- 

 partment of Electrical Engineering at the University of Toledo in 

 Toledo, Ohio, and consultant to the Smithsonian Institution. 



Electrostatic Instruments before 1800 



IT IS THE FUNDAMEN I \I PREMISE of instrument-science 

 that a device for detecting or measuring a physical 

 quantity can be based on any phenomenon associated 

 with that physical quantity. Although the instru- 

 mentation of electrostatics in the 18th century, for 

 example, relied mainK on the phenomena of attrac- 

 tion and repulsion and the ubiquitous sparks and 

 other luminosities of fractional electricity, even the 

 ph\ siological sensation of electric shock was exploited 

 semiquantitatively by Henry Cavendish in his well- 

 known anticipation of Ohm's researches. Likewise. 

 Volta in 1800 1 described at length how the applica- 

 tion of his pile to suitably placed electrodes on the 

 eyelids, on the tongue, or in the ear, caused stimulation 



' A. Yoi.iA. "On the Electricity Excited by the Mere Contact 

 of Conducting Substances of Different Kinds," Philosophical 

 Transactions of the Royc S London i 1800 vol :l1 pp 



403 HI. 



of the senses of sight, taste and hearing; on the other 

 hand, he reported that electrodes in the nose merely 

 produced a "more or less painful" pricking feeling, 

 with no impression of smell. The discharges from 

 the Leydcn jars of some of the bigger frictional 

 machines, such as van Martini's at Leydcn, were found 

 by 1785 to magnetize pieces of iron and to melt long 

 pieces of metal wire. l 



- Sonic little-known but delightful observations in the pre- 

 history of electromagnetism are described in a letter written 

 l.% <. W s, mi! in., from London to the Berlin Academy on 

 |nK ;:. 1769, published ,.s "Sur les phinomenes de I'Anguleil 

 Trerablante" [Nouveaux Mtmoim dt ■■ l' Academic Royaic </-- S 

 ct Belles-lettres. 177ii (Berlin, 1772), pp. 68-74], translated 

 to French from the original German 1 h< let* 

 multitude of experiments with various electric eels. The two 

 observations of electromagnetic interest are thai 

 held by the hand in the eel's tank could be felt quivering even 

 when the lish was stationary several inches away, and a com- 

 p.iss needle showed a deflection, both in the watei n 

 lish. and outside the t.ink. also with the lish stationary. 



I'Al'FR 38: 1 \K 1 II SI I.I.F.CTROMAGNETIC INSTRCMlNIs 



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