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SCIENCE. 



[N. S. Vol. VII. No. 16a 



showed that the thermoelectric order of the 

 metals is not the same at all temperatures. 



The nest important discovery in thermo- 

 electricity was that of Peltier, of the heat 

 generated at the junction of two metals 

 when a current is forced across it against 

 the e. m. f. of the junction. In later years 

 we have the classic researches of Thomson 

 (Kelvin), who added thermoelectric con- 

 vection and the specific heat of electricity 

 and gave the thermoelectric diagram method 

 of representing results. This method was 

 afterwards used and extended by Tait, 

 who added a good deal to our knowledge 

 of thei-moelectric data. Among the large 

 number of others who have worked in this 

 field we may mention Becquerel, Magnus, 

 Matthieson, Leroux and Avenarius. Ther- 

 moelectric batteries of considerable power 

 have been made by Clamond and others. 



In 1827 the celebrated law giving the rela- 

 tion between e. m. f. 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 pos- 

 sible to develop almost completely the 

 mathematical theory as we now have it. 

 Most of the work since Faraday's time has 

 been directed towards quantitative measure- 

 ments 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 experi- 

 mental laws. The laws were afterwards 

 experimentally verified by "Weber. In 1849 



the experiments of Kirchoff 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 sub- 

 ject, which he supplemented with an ex- 

 perimental 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 A. A. A. S. in 1850, but he knew of the 

 effect much earlier, certainly in 1841. Pre- 

 viously the anomalous behavior of the dis- 

 charge 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 appre- 

 ciate 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 dis- 

 charge 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 Hemholtz and Thom- 

 son. In the Philosohphical Magazine for 

 1855 there is paper by Professor W. Thom- 

 son (Kelvin) in which the theory of the 

 discharge of a Leyden jar is discussed and 

 the prediction made that under certain 

 specified conditions the discharge must be 

 oscillatory. A number of similar papers, 

 going back to 1848, treat of similar sub- 

 jects. Henry's results do not appear to 

 have become generally known, and we find 

 the verification of Thomson's prediction 

 in 1857 by Feddersen. A number of other 

 physicists have investigated the subject, 

 the work of Schiller being of particular 



