270 Dr. Wood and Mr. Campbell on the piurnal 



The next point of importance was to determine whether 

 the periodicity was peculiar to lead vessels. Fig. 3 shows a 

 set of curves drawn for zinc and carbon dioxide similar to 

 those already given for lead. Here again the periodicity is 

 quite evident, and the above noted maxima and minima can 



Rff. 3. 



12 \6 



//ou/?3 of th£ o&y. 



Curves for Zinc and Carbon Dioxide. March 5-8. 



all be recognized. One very marked difference in this diagram 

 is the frequent intersection of the curves representing suc- 

 cessive days. This is due to the fact that little or no per- 

 manent increase in the ionization occurred. Several other 

 similar sets were obtained for zinc, the gases used including 

 coal-gas, air, and hydrogen. All the sets showed the same 



