532 Intelligence and Miscellaneous Articles. 



The method is equally serviceable when a long capillary of 

 irregular and appreciable volume joins the bulb with the mano- 

 meter, a condition sometimes unavoidable in practice ; the volume 

 of the capillary may then be separately found by temporarily 

 plugging up its detached end. — American Journal of Science, (4) 

 ii. p. 341. 



ON THE INFLUENCE OF TEMPER ATUEE ON THE REFRACTION OF 

 LIGHT BY METALS. BY C. PULFRICH. 



About five years ago I published a research in the Annalcn*, in 

 which the influence of temperature on the refraction and dispersion 

 of several transparent solids (glasses &c.) was the subject of an 

 extended experimental investigation. In this research, I was 

 able to show by a series of arguments, that the (positive and 

 negative) variations of the refractive indices observed in those 

 bodies could be regarded as the result of the combined (or 

 opposed) action of two causes, change of density and change of 

 absorption. < 



This explanation would not at that time apply to the metals 

 For the enormous increase in the refractive indices with tem- 

 perature (about O0037 for 1° C.) found by Kundt t, could only be 

 asciibed to a great change in the absorptive power of the metals. 

 Observations have, however, so far revealed nothing of such a 

 change in the absorption of metals. They show rather that the 

 metals have only a small variation of absorption. It is in agree- 

 ment with this that the dispersion of metals experiences almost no 

 alteration with the temperature. 



The contradiction arising out of this is solved since Pfliigeri, in 

 a research which has lately appeared, has proved that the value 

 given above for the variation in the refractive indices of the 

 metals must be ascribed to a source of error neglected in the 

 apparatus used by Kundt, and that, as shown by his own measure- 

 ments made with Kundt's apparatus and the same form of 

 experiment, both the refractive index and also the dispersion of the 

 metals undergo no demonstrable changes with temperature. 



The behaviour of the metals can therefore no longer be looked 

 upon as in disaccord with the explanation I have given. — Wiede- 

 mann's Anncden i no. 11, 1896. 



* Wiedemann's Annalen, vol. xlv. p. 609 (1892). 

 t Ibid. vol. xxxvi. p. 824. 

 % Ibid. vol. lviii. p. 493. 



