440 JOURNAL OF THE PLYMOUTH INSTITUTION. 
burnt up by contact with it. Hence places containing much ozone 
are considered healthful. The quantity in air is always very small, 
rarely more than 1 in every 700,000; but it is always found in 
greater abundance in the open country than in crowded towns, and 
in still greater quantities on sea-shores. This may be accounted 
for from the fact that in densely-populated districts the ozone is 
quickly used up in the oxydizing process always going on in 
organic substances which are largely produced in towns; and we 
also know that electricity is one great source from which ozone is 
derived. 
I have just stated that friction between unlike substances and 
evaporation are two of the causes which produce atmospheric 
electricity ; and we in the south-west district have practically an 
unlimited supply from the daily rise and fall of the tides, the 
occasional storms, and evaporation from the surface of the whole 
North Atlantic Ocean. It is also known that ozone is produced 
in far larger quantities where electricity is discharged continuously 
and silently through an atmosphere containing oxygen than where 
electric discharges take place in long flashes, and therefore more 
ozone is produced here than where thunder-storms are more 
prevalent. 
One other circumstance should not be forgotten when speaking 
of the climate of a place. It is this: Sea water holds in solution 
from one-thirtieth to one-fortieth of its volume of air; but there 
is this difference, whilst the atmosphere contains only about 21 
per cent. of oxygen, the air in sea water contains 32 per cent., or 
more than half as much more. Jy agitation we may reasonably 
suppose a portion of the air surcharged with oxygen is given off, 
and during storms the quantity is very likely much increased, and 
the effects on health highly beneficial. This I take is one of the 
chief reasons why a seaside residence is so conducive to improved 
health among invalids. Now in Plymouth, in common with the 
whole south-western district, we have the broad, deep, stormy 
Atlantic as the storehouse whence we draw our supply of this 
element; whilst on the east coast the storehouse is narrowed 
down into the comparatively shallow, calm North Sea, or German 
Ocean. 
I have endeavoured to obtain information to draw comparisons 
between our town and some health resorts in the south of our 
island ; but as I was unable to get the results for the same periods 
