On the Reflection of Electrical Rays. 449 



temperature due to conduction along the bar) can readily be 

 found by experiment ; or deduced by analysis, as in the case 

 of an infinite square bar, where 



d = a&- k * and — = -a*©"*-. 

 dx 



As p may easily be determined by experiment, the equation 



can be used to determine er, as 



" = J ' ■•■■•• ( IX «) 



dx 



If Tait's assumption that a = MT (where M is some con- 

 stant and T the absolute temperature) is true, we might obtain 

 two values of a for two points of the bar, the temperature of 

 which was known, eliminate h from the two equations, and 

 thus obtain a value for M. If we performed the same opera- 

 tion for two other points, we should get another value for M, 

 and could verify Taitfs assumption if this value was equal to 

 the preceding. 



The sources of error in the preceding investigation are due 

 to assuming Newton's law of cooling, to neglecting the change 

 of electrical resistance due to a change of temperature, and to 

 partly neglecting the change of thermal conductivity due to the 

 same cause. 



L. On the Reflection of Electrical Rays. 



By Dr. E. Goldstein*. 



[Plate Vn. figs. 1-8.] 



IT has been usually assumed t that the (rectilinear) electrical 

 rays radiating from the kathode of the discharge of an 

 induction-coil terminate where they impinge upon a solid wall, 

 and that beyond the point in which they cut the wall they 

 cannot propagate themselves in any direction %. The experi- 



* Monatsber. der Konigl. Akademie der Wissenschaften zu Berlin. Trans- 

 lated from a separate impression communicated by the Author. 



t Hittorf, Pogg. Ann. exxxvi. 



t Herr J. Puluj (Wien. Ber. 1880, [2] p. 886) is the only physicist 

 who has assumed a limited power of reflection of the kathode-rays, 

 under the assumption that the kathode-light consists of scattered particles 

 of the electrode, since " it is not intelligible why these should in general 

 suffer no reflection at the wall." The conditions of an experiment made 

 by Herr Puluj to examine whether reflection takes place were not, in my 

 opinion, such that any possible reflection would have been recognizable. 

 That which Herr Puluj considers phosphorescence produced by reflected 

 rays is partly phosphorescence produced by the positive light of the so- 



