306 L. Page — A Century's Progress in Physics. 



shortly after the orbit of the Leonids, or November 

 meteors, was found to be the same as that of Tempel's 

 comet. 



Electromagnetism. — During the eighteenth century 

 much interest had been manifested in the study of elec- 

 trostatics and magnetism. Du Fay, Cavendish, Michell 

 and Coulomb abroad and Franklin in America had sub- 

 jected to experimental investigation many of the phe- 

 nomena of one or both of these sciences, and in the early 

 years of the nineteenth century Poisson developed to a 

 remarkable extent the analytical consequences of the law 

 of force which experiment had revealed. Both Laplace 

 and he made much use of the function to which Green 

 gave the name "potential" in 1828, and which is such a 

 powerful aid in solving problems involving magnetism 

 or electricity at rest. 



Meantime electric currents had been brought under the 

 hand of the experimenter by the discoveries of Galvani 

 and Volta. Large numbers of cells were connected in 

 series, and interest seemed to lie largely in producing 

 brilliant sparks or fusing metals by means of a heavy 

 current. Hare (3, 105, 1821) of the University of Penn- 

 sylvania constructed a battery consisting of two troughs 

 of forty cells each, so arranged that the coppers and 

 zincs can be lowered simultaneously into the acid and 

 large currents obtained before polarization has a chance 

 to interfere. This "deflagrator" was used to ignite 

 charcoal in the circuit, or melt fine wires, and was for 

 some time the most powerful arrangement of its kind. 

 That "galvanism" is something quite different from 

 static electricity was the opinion of many investigators ; 

 Hare considered the heat developed to be the distinguish- 

 ing mark of the electric current. He says: "It is 

 admitted that the action of the galvanic fluid is upon or 

 between atoms ; while mechanical electricity when unco- 

 erced, acts only upon masses. This difference has not 

 been explained unless by my hypothesis, in which caloric, 

 of which the influence is only exerted between atoms, 

 is supposed to be a principal agent in galvanism. ' ' 



Questioning minds were beginning to suspect that 

 there must be some connection between electricity and 

 magnetism. For lightning had been known to make 

 magnets of steel knives and forks, and Franklin had mag- 

 netized a sewing needle by the discharge from a Leyden 



