and Spark-length for Small Values of the latter. 



625 



IY. Influence of the Kind of Metal in the Electrodes upon 

 the Discharge. 



(1) Observations in Air at Atmospheric Pressure with dif- 

 ferent Electrodes. — In order to investigate the effects of the 

 material of the electrodes upon the spark-potential, which 

 was the primary object of the research, observations at atmo- 

 spheric pressure similar to those above given for brass sur- 

 faces were taken with a series of electrodes of exactly the 

 same size and shape but consisting of the following metals : 

 aluminium, silver, bismuth, zinc, platinum, antimony, mag- 

 nesium, nickel. 



Considerable difficulty was experienced with the crystalline 

 metals, antimony, bismuth, magnesium, and zinc, on account 

 of uncertainty of contact. The results with these metals 

 therefore show much more scattering observations than the 

 others, and the slopes of the curves are consequently some- 

 what less reliable. The effect on the discharge is nevertheless 

 so unmistakable that the general conclusion is unavoidable. 

 The table and curve of each metal are given below with the 

 exception of brass, which is found in Table I. and fig. 4 

 (PI. XIII.). A first and second series of observations for 

 each metal, representing readings taken on widely different 

 days, are given in each table and shown separately on each 

 curve. 



Table II. — Aluminium. 



(Fig. 5, PI. XIII.) 



1 

 1st Series. 



2nd Series. 



Distance, 



Potential, 

 volts. 



Distance, 

 A. 



Potential, 

 volts. 



2 



3 



3 



4 



4 



45 



4-5 



4-5 



5 



5 



6-2 



62 



75 



75 



10 



12-5 



150 



210 

 180 

 230 

 240 

 295 

 305 

 290 

 315 

 315 

 335 

 325 

 335 

 325 

 345 

 345 



2 



25 



2-5 



3 



3-5 



4 



5 



5-5 



6 



100 

 140 

 150 



150 

 220 

 280 

 320 

 350 

 350 



