176 ROYAL SOCIETY OF CANADA 


Again, with a spark potential of 500 volts, the readings give:— 



Distance between electrodes Discharge pressure in 
in mm. mm. of mercury. 
1 47 
2 2°4 
3 1:7 
5 “94 
10 “51 
the pressures being in the ratio 9-3: 4:8: 3-3: 1-9: 1. 
The minimum spark potential in hydrogen was about 280 volts 
and the critical pressures corresponding to the different spark lengths 
were: — 





Distance between electrodes Discharge pressures in 
in mm. mm. of mercury. 
1 10°3 
2 5°93 
3 4'02 
5 2°80 
10 1°46 

where the various discharge pressures are once more nearly inversely 
proportional to the distance between the electrodes. 
To indicate further that the law is applicable at all points, a table 
of products similar to those recorded for air was calculated, and is 
given in Table IV. A single curve, Fig. V., represents these five 
sets of readings, and again the close grouping of the different results 
about this common curve shows that the law is equally applicable above 
and below the critical pressure to all spark potentials. 
It is evident, then, that with hydrogen just as with air, Paschen’s 
law is rigidly applicable over the whole range of pressures. 
V. EXPERIMENTS IN CARBON DIOXIDE. 
These further experiments were made with a view to corroborate 
the results already obtained in air and hydrogen. The same apparatus 
as had been used with these two gases again served for the experi- 
rents in carbon dioxide and the distance between the electrodes was 
varied as before, so that readings were obtained at the five different 
