338 A CENTUEY OF SCIENCE 



show that meteoric showers are common in November, 

 and of particular intensity at intervals of 33 or 34 years. 

 He confidently predicted a great shower for Nov. 13th, 

 1866, which not only actually occurred but was followed 

 by another a year later, showing that the meteoric swarm 

 extended so far as to require two years to cross the 

 earth's orbit. H. A. Newton (36, 1, 1888) in America 

 and Adams in England took up the study of meteoric 

 orbits with great interest, and the former concluded that 

 these orbits are in every sense similar to those of the 

 periodic comets, implying that a swarm of meteors 

 originates in the disintegration of a comet. In fact 

 Schiaparelli actually identified the orbit of the Perseids, 

 or August meteors, with Tuttle's comet of 1862, and 

 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 



