6oo THE POPULAR SCIENCE MONTHLY 



tive application of the newly discovered law to the prediction of new 

 phenomena. The first stage is generally the longest, the second the 

 most contradictory and difficult, while the third is the most fruitful and 

 may perhaps be regarded as the most interesting. 



The branch of electrical science to which Ohm's law belongs is now 

 so well advanced into the third stage, into which it may be regarded as 

 having been ushered by Clerk Maxwell, that it is difficult to look back 

 to stages one or two. Yet eighty-five years ago the theory of electricity 

 was in the first stage, and the 3^ears from 1825 to 1860, in some respects, 

 mark the limits of the second. This period includes Ohm's work and 

 that of his immediate successors. 



Ohm's work was made possible by the discoveries of Galvani, Volta, 

 Oersted, Ampere, Seebeck and others, whose researches had so broadened 

 the knowledge of phenomena connected with the galvanic circuit as to 

 show the probability of a connecting theory. The formulation of such 

 a connecting theory is the task to which Ohm set himself, approaching 

 the problem from the experimental side. The workers of the early 

 nineteenth century had already in a measure identified and separated 

 the factors at play in the galvanic circuit. Examples of such factors 

 are : the " contact force " at the terminals of the circuit, the " flow of 

 current" along the wire, the " electroscopic force" between any two 

 points of a circuit, the tendency of electricity to escape into the air, 

 and the polarization of the electrodes. There was, however, a lack of 

 definiteness of ideas, as well as of methods of quantitative measurement. 



It is no small task to select the necessary from among the incidental 

 factors and to express their relation in concise form. Upon this 

 achievement rests Ohm's chief claim to fame. This is not, however, his 

 only claim to consideration, for besides establishing the law which 

 bears his name, he devised mathematical methods for determining the 

 distribution of electricity in a complex system of conductors, for both 

 steady and variable currents. He did much in clearing up the con- 

 ception of such terms as electromotive-force, current and resistance. 

 In fact, he did for Volta what Maxwell later did for Faraday. The 

 contributions of Dr. Ohm to the theory of electricity were therefore 

 many sided. They were accomplished because he was a trained mathe- 

 matician, a skilled experimenter and a keen, logical tliinker. A less 

 trained man could not have completed his work; one less honest would 

 have been misled ere the end was reached. Finally, it is interesting to 

 note that recognition of the value of his labors and of the importance of 

 his law came tardily. Like many others, his work was misunderstood 

 and only late in life did ap])reciation and the ambition of his youth — a 

 university appointment — fall to his lot. 



A complete statement of the law discovered by Pr. Olun involves 

 two independent propositions as follows : 

 I. E/I = B. (1) 



