438 JOURNAL OF THE PLYMOUTH INSTITUTION. 
any covered space ; as, for example, in a room, no matter how high 
the ceiling, nor ina wood. Becquerel proved by ascending Mount 
St. Bernard that the electricity in the air increased with the height 
ascended. Atmospheric electricity has been shown by different 
observers to be greater in quantity in January, and least in June, 
whilst the tension is greater during mists and fogs than when clear. 
Plymouth appears to enjoy an immunity from electrical storms, 
thunder and lightning being but seldom known. ‘Thus whilst 
electricity may be largely generated on our coasts, especially from 
the friction and evaporation already spoken of, and the sky often 
shows tokens of the existence of such large quantities of the fluid, 
yet it is generally carried inland before a violent discharge takes 
place ; and as thunder is seldom, if ever, heard more than fourteen 
miles off, so the storm passes unheeded. I have no doubt that a 
large quantity is silently discharged, through our damp atmosphere, 
and unperceived by us. This I shall show directly is a very fruitful 
source of ozone. Our heaviest rains are those known as thunder 
showers. One of the heaviest I have any record of was on 29th 
July, 1871, between 9°30 and 10 a.m., when in less than half-an- 
hour three-quarters of an inch was registered in my gauge. These 
heavy rains during thunder-storms I can account for only by sup- 
posing the vesicles of water forming a cloud to become receivers, 
and as they are charged with electricity of the same polarity 
(positive, as a rule), they are kept asunder by electrical repulsion, 
just as pith balls are when charged with the same kind of elec- 
tricity ; but when the discharge takes place these vesicles rush 
together, coalescing to form large drops, and heavy rain is the 
result. 
Ozonr.—We come now to a constituent of the atmosphere 
which, though small in quantity, yet plays a most important part 
in the economy of nature. I spoke just now of the peculiar 
sulphurous odour which follows a thunderstorm, and those who 
have worked with a frictional electrical machine may have noticed 
the same smell intensified when the machine is worked. That 
smell is produced by a substance called ozone, so named by 
Professor Schonbien, of Basle, in 1840, from 3fm=I smell. This 
substance has been proved to be oxygen in an allotropical con- 
dition, and in a peculiarly active state. By direct experiment 
described in the Philosophical Transactions for 1856, Dr. Andrews 
