ELECTROT I f ERAPEUTICS.
Up to the time of Franklin's historic kite ex periment (see ELECTRICITY, ATMOSPHERIC) the identity of the electricity developed by rubbing and by electric machines (frictional electricity), with lightning had not been generally lished. Dr. Wall 1807, Abbot Nollet, bee, Gray and Winckler had indeed suggested the resemblance between the phenomena of and "lightning," Gray having mated that they only differed in degree. It was doubtless Franklin, however, who first proposed tests to determine the sameness of the ena. In a letter to Peter Comlinson, London, 19 Oct. 1752. Franklin, referring to his kite experiment, wrote, °At this key the phial den jar) may be charged; and from the tric fire thus obtained spirits may be kindled, and all the other electric experiments be formed which are usually done by the help of a rubbed glass globe or tube,• and thereby the sameness of the electric matter with that of lightning be completely demonstrated.'" (Franklin, ments and Observations on Electricity'). bard, at Marley, near Paris, on 10 May 1742, by means of a vertical iron rod 40 feet long, obtained results corresponding to those recorded by Franklin and somewhat prior to the date of Franklin's experiment.
Franklin's important demonstration of the sameness of frictional electricity and lightning doubtless added zest to the efforts of the many experimenters in this field in the last half of the 18th century, to advance the progress of the science. Amongst those workers may be men tioned Watson, Boze, Smeaton, Le Monnier, De Romas, Jallabert, Beccaria, Cavallo, John Can ton, Robert Symmer, Nollet, Winckler, Rich man Dr. Wilson, Kinnersley, Priestley, Aepinus, Delaval, Cavendish, Coulomb, Volta and Galvani. A description of many of the experiments and discoveries of these early workers in the fields of electrical science and art will be found in the scientific publications of the time; notably the 'Philosophical Trans actions,' Philosophical Magazine, Cambridge Mathematical Journal, Young's
the more important of the electrical experi ments and researches at this period were those of Francis Aepinus, a noted German scholar (1724-1802) and Henry. Cavendish of London, England. To Aepinus is accorded the credit of having been the first to conceive the view of the reciprocal relationship of electricity and magnetism. In his work 'Tentamen Theoria Electricitatis et Magnetismi,) published in Saint Petersburg, 1759. he gives the following ampli fication of Franklin's theory, which in some of its features is measurably in accord with pres ent day views: "The particles of the electric fluid repel each other and attract and are at tracted by the particles of all bodies with a force that decreases in proportion as the dis tance increases; the electric fluid exists in the pores of bodies; it moves unobstructedly through non-electric (conductors), but moves with difficulty in insulators; the manifestations of electricity are due to the unequal distribution of the fluid in a body, or to the approach of bodies unequally charged with the
Aepinus formulated a corresponding theory of magnetism excepting that in the case of magnetic phenomena the fluids only acted on the parti cles of iron. He also made numerous electrical experiments, amongst others those apparently showing that in order to manifest electrical ef fects tourmalin requires to be heated to a tem perature between 37.5° C and 100° C. In fact, tourmalin remains unelectrified when its tem perature is uniform, but manifests electrical properties when its temperature is rising or falling. Crystals which manifest electrical properties in this way are termed pyro-electrics, amongst which, besides tourmalin, are sulphate of quinine and quartz.