366 Intelligence and Miscellaneous Articles. 



the Bristol Coal-basin, &c. It was shown that the occurrence of 

 saline waters was not necessarily connected with the proximity of 

 saliferous New Red rocks, and it was suggested that the saline waters 

 at Swindon escaped from a ridge of Palaeozoic rocks against which 

 the Lower Jurassic rocks abutted, as they do on the Mendip Hills. 



Mr. E. T. Newton said the fossils had been collected with great 

 care by Mr. Stanier and Mr. Elliott, an exact record of depths being 

 kept. He noticed some of the more important species that had been 

 met with and their distribution, especially mentioning that the Am- 

 monites from the Oxford Clay were nearly all from greater depths 

 than 400 feet. 



L. Intelligence and Miscellaneous Articles. 



ON THE RESISTANCE IN THE VOLTAIC ARC. BY E. EDLUND. 



TE we measure the apparent resistance of the voltaic arc in the 

 •*- ordinary way, we find that it consists, as it were, of two parts, 

 one of which is independent of the length of the arc, and the other is 

 proportional to it. If we call the resistance w t the length of arc Z, 

 while a and b are two constants, then w = a + bl. This holds if 

 the current strength is kept constant while the length of the arc is 

 changed. The behaviour of the constants a and b is in so far 

 different that b is less when the current increases, while a is almost 

 independent of the strength of the current, and of the electromotive 

 force of the source of electricity ; it is only when this is so much 

 diminished that an arc light is scarcely formed that the value of a 

 becomes less. These observations of mine* have been confirmed by 

 experimenters in recent times. 



The question may be put whether this constant a represents a 

 resistance of transition, which takes place at the surface of contact 

 of the electrodes and the air, or whether it has its origin in an 

 electromotive force, for the diminution in the strength of the 

 current expressed by a might be explained by either of these 

 assumptions. Erom the reasons given in the researches in 

 question, and to which we here refer, it follows that a represents 

 an electromotive force, which acts in opposition to the principal 

 current. 



Of all investigations on this subject published in the last few 

 years, we shall only call attention to the following. 



Erolichf, who in his investigation made use of observations 

 made in the laboratory of Siemens and Halske, came to the 

 conclusion that either of the assumptions are reconcilable with 

 these observations, though he seems inclined to think that the 

 constant a represents an electromotive force, as well as a re- 



* Pogg. Ann. vol. cxxxi. p. 586 (1867) ; vol. cxxxiii. p. 353 ; vol. cxxxiv. 

 pp. 250, 337 (1868) ; and vol. cxxxix. p. 354 (1870). 

 t Eketrotechn. Zeitschrift, vol. iv. p. 150 (1883). 



