J\aiIi(U)i Biidiat'ion and Contact Electriciiij. 



705 



The results of these experiments are ^iveii in Table II. 

 A\ hen careful attention \vas paid to ])olishin<>' the metal sur- 

 faces, readinos taken on diti'erent days only differed by two 

 or three divisions. 



Table II. 



Deflexion for C^ark Cell, +125, -125. 



Metal on Lower Plate. 



Zinc 



Aluminium 



Tin 



Bismuth . 

 Antimony . 



Brass 



Iron 



Copper .... 



Silver 



Gold 



Platinum . 



Potential 



of Upper 



Potential of Lower 



PL-) 



te. 



Plate. 



Deflexion. 



Volts. 



Deflexion. 



Volts. 

 -15 



+ 5 



+ 05 



-13 



+ 5 



+ •05 



-12 



-•u 



— 5 



-^05 



+ 6 



+ 07 



- 6 



-•07 



-f 10 



+ 11 



- 8 



-•09 



+ 14 



4-ib 



-11 



-•12 



+ 20 



+ 23 



-12 



-•14 



+ 20 



+ 23 



-13 



-•15 



+ 22 



+•25 



-17 



-•20 



+ 29 



+ 33 



-17 



-•20 



4-31 



+ 36 



-21 



-•24 



+35 



+ 40 



It would doubtless have been better if the lower electrode 

 had been composed wholly of the metal to be examined, but 

 this would have restricted the number of metals that could be 

 used. The simpler plan of laying the metal plate on the 

 lead electrode gives a smaller potential-difference, but could 

 scarcely affect the relative order in the voltaic series. In 

 order to observe the increased potential in one case an elec- 

 trode was prepared of tlie same size as the lead electrode, but 

 consisting wholly of brass. The potential-difference in this 

 case amounted to *32 volt_, as compared with "23 volt when a 

 brass plate was placed on the lead electrode. 



The plates used in these experiments were of commercial 

 metal, and therefore not chemically pure. 



An inspection of the results in Table II. will show that the 

 metals fall into their places in the voltaic series, as given for 

 example by Ayrton and Perry (Phil. Trans. Roy. Soc. 1880, 

 p. 15). The only difference is in the case of brass, which we 

 find between iron and antimony, but this may well be due to 

 a difference in composition. 



Potential-Diference in an Exhausted Vessel. 



It appeared to be of interest to determine whether there 

 would be any alteration in the potential-difference between 



