274 Dr. Wood and Mr. Campbell on the Diurnal 



values of the two quantities. They are so chosen as to give 

 nearly the same range in the two cases. 



Fie. 7. 



Lead was found to give a somewhat greater mean daily 

 range than zinc, but the smaller total ionization of the zinc 

 made the proportional range greater for zinc than for lead. 

 In nine successive days in August the value of this ratio 

 was 0*12, 0-09, 0-17, O'U, 0-18, 0'16, 0;12, (H4, 0*09; this 

 gives a mean of 0'12, so that the variation in the ionization 

 in the course of one day amounts to about 12 per cent, of 



