268 Dr. Wood arid Mr. Campbell on the Diurnal 



when the vessel contained coal-gas. Coal-gas is so uncertain 

 in composition that little importance is attached to this 

 result. Air was enclosed in the zinc vessel on the 10th of 

 August this year, and its ionization measured on our scale 

 was found to be 0*513. It was left enclosed until the 12th 

 of October, and the ionization was then 0*521. The behaviour 

 of the tin was similar to that of the lead, and showed a 

 gradual increase in the ionization extending over the whole 

 period of the investigation. 



By far the most interesting feature of the curves, however, 

 is their periodic character. This is quite well marked in the 

 curves for lead, indeed it was in the curves for lead and 

 carbon dioxide that it was first noticed. It will be seen that 



Fig. 1. 



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JO 15 



ffou/?s or the oay. 



Lead and Carbon Dioxide. 



20 



24- 



in fig. 1 each curve shows a very marked maximum at a time 

 varying from 21 hours (9 p.m.) to 23 hours (11 p.m.) and a 



