Intelligence and Miscellaneous Articles, 77 



of the light which this distant planet receives is alone available for 

 the purposes of its economy. 



The photographic researches of Mr. De la Rue and others show 

 that the rays of high refrangibility, which are specially powerful in 

 producing chemical action, are similarly affected *. At present we 

 know nothing of the reflective power of the planets for those rays 

 of slower vibration which we call heat. — Monthly Notices of the 

 Royal Astronomical Society, March 8, 1867. 



ON A NEW METHOD OF DETERMINING THE RESISTANCE OF GAL- 

 VANIC CIRCUITS. BY PROF. V. WALTENHOFER. 



The methods of determining the electromotive force and the re- 

 sistance of metallic circuits afford a very high degree of certainty 

 and accuracy, while the present methods of measuring the resist- 

 ance of galvanic elements are very faulty. Even under the most 

 favourable circumstances they are destitute of accuracy, and in many 

 cases are quite useless. The latter is more especially the case with 

 inconstant elements, in regard to which Poggendorff has shown that 

 the use of Ohm's method yields greater values for the internal resist- 

 ance the greater the external resistances ; so that the entire method 

 in such cases becomes quite deceptive. 



It has been hitherto assumed that this peculiar deportment of in- 

 constant elements arises from polarization, inasmuch as from one 

 experiment to the next it acts unequally in opposition to the elec- 

 tromotive force of the element. But the author has calculated that 

 this assumption is inadequate for explaining the said phenomenon, 

 since polarization, so far as its dependence on the intensity of the 

 current is understood, must behave quite differently when the resist- 

 ance of the circuit is constant. The author concludes herefrom that 

 the changes of resistance in question which are observed in the case 

 of Ohm's method are not simply apparent, produced by polarization, 

 but must be occasioned by an actual dependence of the resistance 

 of the circuit on the intensity of the current, — which then is easily 

 explained, taking into account the manifest dependence of the so- 

 called resistances of passage {U eb er g any swid erst and e) on the inten- 

 sity of the current. 



If this assumption be correct, there must be circuits whose internal 

 resistance is less with increasing external resistances (that is, with 

 decreasing intensity), as well as those in which the opposite is 

 the case, according as the resistances of passage, conditioned by the 

 chemical nature, and arrangement of the materials of the element, 

 occasion one deportment or the other. 



Without entering here more minutely upon this point, it may be 

 sufficient to remark that experimental investigations on these and 

 other important points in the theory of the circuit presuppose the 

 possibility of measuring the resistances of galvanic circuits quite in- 

 dependent of the influence of polarization, — which of course is only 

 possible with very small intensities. But if these very small inten- 



* Profesor G. Bond states that " the moon, if the constitution of its sur- 

 face resembled that of Jupiter, would photograph in one fourteenth of the 

 time it actually requires." — Ibid. p. 223. 



