and Spark-length for Small Values of the latter. 623 

 Table I.— Brass Electrodes in Air. (Fig. 4, PL XIII.) 



Pressure 



Pressure 



Pressure 



Pressure 



Pressure 



Atmos 



aberic. 



40 



cm. 



25 



3111. 



15 



cm. 



1 cm. 



Dist. 



Spark- 



Dist. 



Spark- 



Dist. 



Spark - 



Dist. 



Spark- 



Dist. 



Spark- 



in 



Poten. 



in 



Poten. 



in 



Poten. 



in 



Poten. 



in 



Poteu. 



Wave- 



in 



Wave- 



iu 



Wave- 



in 



Wave- 



in 



Wave- 



in 



lgths. 



Volts. 



lgths. 



Volts. 



lgths. 



Volts. 



Igths. 



Volts. 



lgths. 



Volts. 



1-5 



95 



20 



110 



25 



165 



20 



225 



30 



240 



30 



175 



20 



175 



30 



160 



3-0 



210 



30 



270 



35 



225 



25 



190 



30 



170 



4-0 



285 



40 



345 



4-0 



275 



30 



150 



30 



175 



4-5 



345 



4-5 



345 



4-2 



325 



3-2 



265 



4-0 



305 



50 



340 



5-0 



350 



4-5 



320 



40 



305 



5-0 



340 



7-5 



340 



7-5 



350 



50 



345 



4-5 



335 



7-5 



340 



100 



350 



150 



350 



60 



345 



4-7 



345 



10-0 



345 



125 



350 



250 



350 



7-5 



345 



50 



355 



12-5 



345 



17-5 



350 



500 



350 



100 



345 



60 



317 



175 



345 



25-0 



350 



750 



350 



12-5 



350 



7-5 



340 



250 



350 



37-5 



350 







150 



360 



10-0 



340 



350 



350 



42-5 



350 







17-5 



355 



10-0 



350 



375 



355 



50-0 



350 







250 



400 



150 



350 



40-0 



3o0 



60-0 



360 







37-5 



430 



17-5 



350 



40-0 



370 



65-0 



375 











200 



350 



400 



370 



750 



410 











22-5 



350 



42-5 



390 















22-5 



345 



50-0 



390 















25-0 



365 



67-5 



430 















27-5 



365 



















375 



375 



















37-5 



395 



















50-0 



415 



















50-0 



420 















(2) Minimum Spark-Potential for Curved Electrodes. — 

 According to Peace and Carr, at a given distance between 

 the electrodes a discharge will take place at the minimum 

 spark-potential (characteristic of the gas) if the pressure has 

 a certain value called the " critical pressure." Now if either 

 the distance or the pressure he decreased while the other is- 

 kept constant, it will be found necessary to increase the 

 potential in order to produce a discharge. These facts were 

 observed with the use of plane electrodes; but where one of 

 the electrodes is spherical as in this case, it will be seen, as 

 indeed Carr pointed out, that when the nearest point of the 

 curved surface is closer to the flat electrode than the distance 

 at which the discharge takes place with a potential equal to. 

 the minimum value, the spark can still pass at this potential 

 from a point further out on the curved surface. 



It will be seen therefore, that with such electrodes the 

 discharge-potential, instead of passing through a minimum, 



