GALVANISM. 



Cilbert published a treatise on magnetism, in which 

 he first applied the term poles to the magnet, and 

 he speculated on the nature of the earth's mag- 

 netism, and on magnetism generally. The astron- 

 omer-royal, H alley, published the first magnetic 

 charts in 1701. Some twenty years after, Graham, 

 the celebrated instrument-maker of London, dis- 

 covered the daily variation of the compass. 

 Armatures were not used before 1750, when 

 special attention was given to new processes of 

 increasing and preserving magnetism. In 1770, 

 the magnetism of cobalt and bismuth was first 

 observed. About the beginning of this century, 

 Humboldt inaugurated the system of careful ob- 

 servation of the magnetic elements, and in 1835, 

 stations were established throughout Europe for 

 this purpose. In 1831, Captain Ross discovered 

 the north magnetic pole, and Barlow in the same 

 year suggested an electric theory of the earth's 

 magnetism. Colonel Sabine, in 1837, first pub- 

 lished an isodynamical chart of the globe, shewing 

 all places of equal magnetic intensity. In 1845, 

 Faraday discovered diamagnetism ; and ten years 

 later, Tyndall shewed that a diamagnetic body 

 assumes a polarity similar in action but transverse 

 to that of a magnetic body when under magnetic 

 influence. More recently, Tyndall has discovered 

 that a close relation exists between the optic axes 

 of crystals and the positions in which they set 

 between the poles of a powerful magnet. 



Electricity. The science of electricity dates 

 from 1600, when Gilbert wrote his celebrated 

 treatise. He has given us the earliest specula- 

 tions on the subject, and bequeathed to us the 

 name electricity itself. In 1672 was constructed, 

 by Otto von Guericke of Magdeburg, the first 

 electrical machine. It was in the humble form 

 of a globe of sulphur, turned by a handle, and 

 rubbed with a cloth in the hand. This Hawksbee 

 replaced, in 1709, by a glass cylinder; and in 1744 

 a fixed cushion-rubber was first used by Winkler, 

 a Leipsic professor. Accident led to the dis- 

 covery of the Leyden jar by Musschenbroeck of 

 Leyden, in 1746. While holding in one hand a 

 glass flask filled with water, which he had just 

 charged from a machine, he happened with the 

 other hand to touch a wire which communicated 

 with the water. He received a very violent shock 

 so violent, that he declared he would not have 

 another for the kingdom of France. In 1747, 

 Franklin explained the action of the Leyden jar, 

 and in 1752 made his well-known kite experiment. 

 The nature of induced electricity occupied the 

 attention of Wilke, yEpinus, and Canton about 

 this time. In 1768, Ramsden first constructed a 

 plate-machine ; and in 1780, Nairne brought his 

 cylinder-machine into notice, its value being that 

 it gave either positive or negative electricity. 

 Volta invented the electrophorus in 1775, and in 

 1782 his well-known condenser. About 1787, 

 Coulomb investigated the laws of electric attrac- 

 tion and repulsion. After this, the science was 

 thrown in the shade by galvanism, until Faraday, 

 in 1837, made some invaluable researches on 

 statical induction, and shewed its action to be 

 universal. More recently, Reiss, Tcepler, and 

 Holtz have paid special attention to the electricity 

 of friction ; and the novel induction-machines of 

 the latter two have rekindled the curiosity of 

 experimenters. 



Galvanism, Current Induction, firv. Little idea 



could Galvani have had that his accidental dis- 

 covery, in 1786, was the embryo of one of the 

 grandest sciences which the human mind has 

 developed. It was five years ere he published 

 his researches, and then they were thrown as an 

 apple of discord among the philosophers of the 

 time. Volta next year (1792) discarded Galvani's 

 explanation, and gave in place his now equally 

 famous contact theory ; while within the same 

 year another professor, Fabroni, of Florence, 

 suggested chemical action as having some share 

 in the phenomenon. With the last year of the 

 century (1799) came Volta's crowning evidence of 

 the truth of his reasoning, his zinc and copper 

 pile, which has proved a boon to science and to 

 man. Volta sent the news of his discovery in 

 1800 to Sir Joseph Banks, in England, and within 

 a few weeks fresh discoveries commenced. Carlisle 

 and Nicholson decomposed water and several of 

 the salts by means of the pile, and every year saw 

 some new application of this remarkable contriv- 

 ance. Davy traced the origin of the electricity 

 to chemical action, and Wollaston went farther ; 

 he even attributed frictional electricity to chemi- 

 cal action, and proved that it can be made to 

 give chemical effects. The voltaic pile was 

 improved by Cruikshank, who gave it the trough 

 form in 1802, which it subsequently assumed in 

 all experiments. In 1806, Davy discussed fully 

 electro-chemical decomposition ; and in 1813, by 

 aid of the enormous battery at the Royal Institu- 

 tion, he discovered the wonders of the electric 

 light. Even as early as 1808, Sommering pro- 

 posed to effect telegraphic signalling by an electro- 

 chemical process ; but it was not till the Dutch 

 philosopher CErsted discovered, in 1820, the de- 

 flection of a magnetic needle by the current, that 

 the basis of our present system was laid. To 

 the same year belong several remarkable ideas. 

 Schweigger followed up the discovery of CErsted 

 in a few months with his invention of the galvan- 

 ometer ; Ampere proposed the deflections of its 

 needle as a means of telegraphing through a line 

 of wire, but, strange to say, it was put to no prac- 

 tical test for a dozen years more ;. and, lastly, 

 Ampere produced his electric theory of magnet- 

 ism, which has been so remarkably fertile in 

 results. 



The immortal Faraday now appears on the field, 

 to surpass by his achievements even Davy, his 

 illustrious master. In 1831-1832, he published, 

 in the Philosophical Magazine, his researches on 

 electricity, by which he made known his discovery 

 of volta-electric or current induction, and also of 

 magneto-electric induction. His discovery was 

 embodied in the magneto-electric machines of 

 Pixii, Saxton, and Clarke, which appeared in suc- 

 cession between the years 1832 and 1836. About 

 the same time, Faraday established the definite 

 laws of electro-chemical decomposition, and traced 

 the spark, which appears on breaking a long 

 circuit, to the extra current^ or its own induction. 

 These years were remarkable in the history of 

 electricity, for, in 1833, Ampere's idea of a tele- 

 graph was first put to a practical test Gauss and 

 Weber, at Gottingen, actually established an 

 electric telegraph, about two miles long, between 

 their magnetical observatory and their physical 

 cabinet The indicator was a reflecting galvan- 

 ometer, and they made up an alphabet of right 

 and left deflections of the needle. This, however. 



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