THE DEVELOPMENT OF ELECTRICAL SCIENCE. 223 



force resistance and current was published by Ohm in a paper on the 

 mathematical theory of the galvanic circuit. The theory has been 

 sometimes criticised, but there seems to be absolute certainty that the 

 law is almost exact, and it has proved of the greatest importance in the 

 further development of the subject of electric measurements. 



The subject had about the middle of the century reached a stage in 

 which it was possible to develop almost completely the mathematical 

 theory as we now have it. Most of the work since Faraday's time has 

 been directed toward quantitative measurements and the furnishing of 

 exact data to answer questions as to how much in various cases. F. E. 

 Neumann discovered what he called the potential function (now called 

 the coefficient of self and mutual induction) of one current on another 

 and on itself, and succeeded in giving a theory of induction which was 

 in accordance with the experimental laws. The laws were afterwards 

 experimentally verified by Weber. In 1849 the experiments of Kir- 

 choff on the absolute value of the current induced in one circuit by 

 another, and in the same year Edlund's experiments on self and mutual 

 induction are important. In 1851 Helmholtz gave a mathematical 

 theory of this part of the subject, which he supplemented with an 

 experimental verification. 



One of the most important of the series of experiments made by 

 Henry was on the oscillatory character of the discharge from a Leyden 

 jar. This he discovered from the effect of the discharge on a steel 

 needle surrounded by a coil, through which the current was made to 

 pass. The results of these experiments were communicated to the 

 American Association for the Advancement of Science in 1850, but he 

 knew of the effect much earlier, certainly in 1841. Previously the 

 anamolous behavior of the discharge of a jar when used to magnetize 

 steel needles had been noticed, but was attributed, as I believe, to 

 some peculiarity of the steel. Henry was the first to appreciate the 

 true reason, although he could hardly at that time be expected to see 

 the great importance of his discovery. 



Helmholtz, in 1847, suggests that the discharge of Leyden jars may 

 be of the nature of a backward and forward movement. There is a 

 curious parallelism in the work of several investigators about this time, 

 and particularly in that of Helmholtz and Thomson. In the Philosoph- 

 ical Magazine for 1855 there is a paper by Prof. W. Thomson (Kelvin) 

 in which the theory of the discharge of a Leyden jar is discussed and 

 the prediction made that under certain specified conditions the dis- 

 charge must be oscillatory. A number of similar papers, going back 

 to 1848, treat of similar subjects. Henry's results do not appear to 

 have become generally known, and we find the verification of Thom- 

 son's prediction in 1857 by Feddersen. A number of other physicists 

 have investigated the subject, the work of Schiller being of particular 

 value. The recent applications will be referred to later. 



The mathematical theory of electrostatics and magnetism was greatly 



