166 
I shall draw more especial attention to these figures in 
reference to the air, for they show the comparative impurity of the 
air in different localities ; but in examining the rain further, it may 
be interesting to show the considerable difference in the compo- 
sition of the rain in this district at different periods and in different 
situations. The difference is due chiefly to the varying extent of 
contamination by sea-spray. Some time ago I constructed gauges 
at different places in order to determine the amount of saline 
matter carried in the air from the sea, and thus conveyed to the 
land. I found marked differences with only slight alterations of 
situation. Thus— 
Parts per 100,000. 
Collected about 400 yards Collected nearly one mile 
from the sea, - from the sea. 
Sodium Chloride 12°20 ao 2°45 
Magnesium Chloride 3°43 su 0°67 
Again, according to the stormy character of the weather, we have 
variations in the composition of the rain in different months; and 
occasionally it is very considerably contaminated with ordinary 
saline substances, such as common salt. Thus— 
Grains per Gallon. 1876. 
—— 
Total Solids... aie ..-| 4:000 | 5°173 | 4°666 | 2°710 
Loss on Ignition pa ...| 0°014 | 0017 | 0:010 | 0:010 | 0:100 
Fixed solid residue... ...| 3°986 | 5°156 | 4:656 | 2°700 | 6636 
Chlorine, equal to Sodium : : : : ; 
ae 1-092 | 2-135 | 1480 | 0-786 | 2:847 
The rain is in every case our primary source of water-supply, 
for whether we collect the water which falls on the roofs of houses, 
or from streams and rivers, or from deep or shallow wells, it is 
only rain more or less contaminated since it has fallen. Mr. G. J. 
Symons, F.R.S., who has obtained for several years rainfall statistics 
