132 
wet and dry bulb hygrometer, which I have had in use for 
16 years, and reductions based upon Glaishers humidity 
tables. In the foregoing table the averages of the relative 
amount of moisture in the atmosphere are given in the last 
column. Of course the order of the amounts is inverse to 
the ratios of rainfall, one being positive and the other 
negative. The striking resemblance between facts shown 
by each is at once obvious. I have, however, projected 
them in the following diagram. The irregular line marked 
(a) represents the rainfall ratios, and the one marked (6) 
the mean relative amount of humidity. Hence I infer 
that the maximum of dry air on the ground is in May, 
June, and July, and the minimum in November, December, 
and January. These periods of maximum and minimum 
are closely allied to similar periods of ozone results. 
In the next table I give the fall of rain for 1875 during 
the day, from 8 a.m. to 8 p.m., and the fall during the night 
from 8 p.m. to 8 a.rn. The results of these observations for 
1874 I pointed out were exceptional, as in every pre- 
vious year since I instituted them the day-fall had always 
been greater than the night-fall. The last year gives the 
original kind of results, and the day-fall exceeds the night, 
and by about the same amount as the reverse of 1864. 
The excess of the day-fall over the night of last year was 
2*517 inches, or about 13 per cent. 
