( 813 ) 



As heat-rays have only an exceedingly slight effect, and, as I 

 ascertained later on in conjunction with Mr. Vas Nunes, also the 

 ultraviolet light emitted by cadmium poles causes only a small 

 increase of the conductivity, the dependence of wave-length and 

 decrease of resistance is evidently represented by a curve whose 

 minima lie in the nltrared, in the green and in the ultraviolet, and 

 whose maxima are situated in the red and in the blue part of the 

 spectrum 1 ). 



Later on when the determinations of the resistance of this sub- 

 stance will have led to favourable results, we shall make some closer 

 communication on the relation between thermal and electric motion 

 in this conductor. 



§ 7. The phenomenon discovered here reminds strongly of that 

 observed for selenium 2 ). It is, however, noteworthy, that though the 

 dependence of the increase of the conductivity on the radiation of 

 light, and even on the wave-length of the light manifests itself in a 

 perfectly analogous way to that for antimonite, yet the two differ in 

 some respects. First of all for the selenium polymorphous changes, 

 and the displacement of equilibrium attending them play an im- 

 portant part; then, however, the resistance always decreases here 

 with rise of temperature, so exactly the reverse of what happens in 

 my investigations, in which moreover there is no question whatever 

 of polymorphous changes, as far as is known. An analogy between 

 the two cases is to be found in the fact already discovered by 

 Adams 8 ), that the resistance decreases with rising electromotive force, 

 also after continued action of it ; such a deviation from the law of 

 Ohm is also found for the antimonite. 



On the other hand the behaviour of antimonite from Japan seems 

 to present a closer analogy with that of the crystallised tellurium; 



l ) Though it is not intended as an explanation, I will yet call to mind that it 

 follows from Müller's investigation (N. Jahrb. f. Miner, u. s. w. Beil. Bd. 17, 187—251) 

 on the optical constants of the antimonite from Japan, that the indices of refraction 

 Wj and w 3 have their maximum values exactly for the green rays (between the 

 lines E and F) (viz. n x = 5,47— 5,53 and n 2 = 4,52— 4,49), while also the double 

 refraction reaches its maximum value for these rays. The polarisation of the 

 reflected rays is right-elliptic (negative). However, on using polarized light, we could 

 not find any influence of the direction of vibration: the variation of the electric 

 resistance was in the two cases the same. (Added in the English translation). 



■) G. Wiedemann, Die Lehre v. d. Eleklricitat (1882). I. p. 514-553). 



sj Sale, Phil. Mag. [4]. 47. 216. (1874); Pogg. Ann. 150. 333; Chem. News. 

 33. 1. (1876). 



«) Adams, Phil. Trans. 157.; Pogg. Ann. 159. 621. (1876), Phil. Mag. [5]. 1. 115 



