460 Intelligence and Miscellaneous Articles. 



lens of long focus, so that Fraunhofer's lines were visible on a 

 paper screen. When the paper covered with the platinocyanide of 

 barium was substituted for the ordinary paper screen, nearly the 

 whole portion on which the blue rays fell appeared of an unaltered 

 blue colour ; but in this blue part of the spectrum, three isolated 

 green fluorescent bands appeared. One of these fluorescent bands 

 falls with its middle upon Fraunhofer's line G; the other two lie 

 between G and F, and the middle of these bands corres])onds with 

 the wave-lengths 0-0004G2, 0'000446, and 0-000430 millim. The 

 rays of light of the lengths of undulations just mentioned conse- 

 quently produce a green fluorescence upon platinocyanide of barium ; 

 whilst the intervening lengths of undulations, 0'000454 and 0-000438 

 millim., as well as rays of the length of undulation, 0'000420 millim., 

 produce no fluorescence upon this substance. 



An uninterrupted green fluorescence only begins at that spot of 

 the spectrum which nearly corresponds with a length of undulation 

 of 0'000410 millim. I am unacquainted with any analogous phsc- 

 nomenon. — PoggendorfF's Annalen, 1858, No. 8. p. 649. 



ON THE INCREASE OF THE ELECTRICAL RESISTANCE OF THE 

 METALS WITH THE TEMPERATURE. BY R. CLAUSIUS. 



In the May Number of PoggendorfF's Annalen there is an interesting 

 memoir by Arndtsen upon the resistance of metals at various tem- 

 peratures, in which the author arrives at the result, that in the 

 simple metals investigated by him, with the exception of iron, the 

 resistance increases uniformly with the temperature, and moreover, 

 that the proportional increase in the diflferent metals varies but little. 

 If the resistance at the freezing-point be called 100, the numbers 

 representing the increase for 1° C. (1°'8 F.) in the six simple metals 

 investigated, lie, with the exception of iron, between 0"327 and 

 0'413*; and Arndtsen adds, that if absolutely pure metals were 

 employed, and the investigations were carried on still more carefully, 

 perfectly accordant numbers would probably be obtained. 



On glancing at these numbers, it struck me that they closely 

 apjnoach the coefficients of expansion of permanent gases. If we 

 leave out of consideration the quadratic member occurring in iron, 

 and take the mean of the whole of the first coefficients, we obtain 

 for the resistance w' at the temperature t, compared with the resistance 

 10° at the freezing-point, the formula 



from which it would follow that the resistance of the simple metals 

 in the solid state is nearly in proportion to the absolute temperature. 

 Although the number of metals investigated by Arndtsen is still 

 too small, and the agreement of the numbers too imperfect to enable 

 us to arrive at a safe conclusion, still I think that this observation 

 may perhaps be of some interest, and furnish an inducement to 

 further investigations. — PoggendorflF's Annalen, 1858, No. 8. p. 650. 



* The numbers found by Matthiessen for potassium and sodium in the 

 solid state also fall between these limits. 



