The useful instruments that emerged from all of 

 this experience were various deflecting "electrometers" 

 and "electroscopes"' (the words were not carefully 

 distinguished in use), including the important gold- 

 leaf electroscope ascribed to Abraham Bennet in 

 1787. 3 



In 1786, Galvani first observed the twitching of 

 the legs of a dissected frog produced by discharges 

 of a nearby electrostatic machine, thereby revealing 

 still another "effect" of electricity. He then dis- 

 covered that certain arrangements of metals in con- 

 tact with the frog nerves produced the same twitching, 

 implying something electrical in the frog-metal situa- 

 tion as a whole. Although Galvani and his nephew 

 Aldini drew from these experiments erroneous con- 

 clusions involving "animal electricity," which were 

 disputed by Yolta in his metal-contact theory, it 

 is significant from the instrumentation point of view 

 that the frog's legs were unquestionably by far the 

 most sensitive detector of metal-contact electrical 

 effects available at the time. Without their interven- 

 tion the development of this entire subject-area, 

 including the creation of chemical cells, might have 

 been delayed many years. Volta himself realized 

 that the crucial test between his theory and that of 

 Galvani required confirming the existence of metal- 

 contact electricity by some electrical but nonphysio- 

 logical detector. He performed this test successfully 

 with an electroscope, using the "condensing" tech- 

 nique he had invented more than a decade earlier. 



Instrumenting Voltaic or Galvanic 

 Electricity, 1800-1820 



In his famous letter of March 20, 1800, written in 

 French from Como, Italy, to the president of the 

 Royal Society in London, Volta made the first public 

 announcement of both his "pile" (the first English 

 translator used the word "column"), and his "crown 

 of cups" (the same translator used "chain of cups" 

 for Yolta's "couronne de tasses"). The former 

 consisted of a vertical pile of circular disks, in which 

 the sequence copper-zinc-pasteboard, was repeated 

 10 or 20 or even as many as 60 times, the pasteboard 

 being moistened with salt water. The "crown of 

 cups" could be most conveniently made with drinking 

 glasses, said Volta, with separated inch-square plates 



of copper and zinc in salt water in each glass, the 

 copper sheet in one glass being joined by some inter- 

 mediate conductor and soldered joints to the zinc in 

 the next glass. 



Volta considered the "crown of cups" and the "pile" 

 to be essentially identical, and as evidences of the 

 electrical nature of the latter, said : 



. . . if it contains about 20 of these stories or couples 

 of metal, it will be capable not only of emitting signs 

 of electricity by Cavallo"s electrometer, assisted by a 

 condenser, beyond io° or 15 , and of charging this 

 condenser by mere contact so as to make it emit a spark, 

 etc.. but of giving to the fingers with which its extrem- 

 ities (the bottom and top of the column) have been 

 touched several small shocks, more or less frequent, 

 according as the touching has been repeated. Each 

 of these shocks has a perfect resemblance to that slight 

 shock experienced from a Leyden flask weakly charged, 

 or a battery still more weakly charged, or a torpedo in 

 an exceedingly languishing state, which imitates still 

 better the effects of my apparatus by the series of repeated 

 shocks which it can continually communicate. 4 



The "effects" provided by Volta's pile and crown- 

 of-cups are therefore electroscope deflection, sparks, 

 and shocks. Later in the letter, he describes the 

 stimulation of sight, taste, and hearing as noted 

 earlier, but nowhere does he mention chemical 

 phenomena of any kind, or the heating of a wire 

 joining the terminals of either device. Hence, except 

 for the additional physiological responses, he adds 

 nothing to the catalog of observations on which in- 

 struments might be based. His familiarity with the 

 moods of the torpedo (electric eel) seems to be intimate. 



The reading of Volta's letter to the Royal Society 

 on June 26, 1800, its publication in the Society's 

 Philosophical Transactions (in French) immediately 

 thereafter, and its publication in English in the 

 Philosophical Magazine for September 1800, s gave 

 scientists throughout Europe an easily constructed 

 and continuously operating electric generator with 

 which innumerable new physical, chemical, and 

 physiological experiments could be made. Editor- 

 engineer William Nicholson read Volta's letter before 

 its publication and, by the end of April, he and surgeon 

 Anthony Carlisle had built a voltaic pile. Applying 



'Abraham Bennet, Philosophical transactions of the Royal 

 Society of London I 1787), p. 26. 



4 Op. cit. (footnote 1 ), p. 403. 



« Philosophical Magazine (1800), vol. 7, pp. 289-311. [For a 

 facsimile reprint, see Cahani-Votta (Bern Dibncr's Burndy 

 Library Publication No. 7), Norwalk, Connecticut, ITiL'.i 



124 



BULLETIN 24<): CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



