PRESIDENTIAL ADDRESS. ~— 123° 
Although the characteristic odour produced by certam 
natural electric phenomena seems evidence of its presence, 
at least for the time, some doubts have recently been thrown 
upon its existence in the air, as a normal constituent. How 
far it will retain the place of honour it has so long held, or 
be forced to give place to peroxide of hydrogen, as a normal 
constituent of the atmosphere, we must leave for future 
‘investigation to decide. 
The production of ozone on the larger scale has had much. 
attention bestowed upon it of recent years, and it would 
seem as if an important new chemical industry were thus 
being established. 
A search for other constituents of the normal air was made 
by various methods. It was recognised that rain, m fall- 
ing through the atmosphere, must collect not only normal 
gases, but many of the impurities that were known to neces- 
sarily exist there. Extended mvestigations, involving 
analyses of the rain from many different localities by many 
different workers, demonstrated the presence of those sub- 
stances we should just expect to find, chiefly common salt in 
the air over the sea, the sulphates and ammoniacal salts in- 
creasing as towns are approached. 
Successful attempts were made by Angus Smith and others 
to imitate the action of the rain by washing the air and 
analysing the air-washings. In this way soluble substances 
were collected and crystallised out, solid substances measured 
and counted, and determinations made of the organic 
matter. 
Living organisms, both nocuous and innocuous, were found 
to exist, and their collection and examination constitute a 
special study by itself—the bacteriology of the air.  For- 
tunately, however, these micro-organisms seem to be present 
only in the lowest strata of the atmosphere, whither they 
are raised by air-currents. They are incapable of rising 
into the air without such assistance. They increase with 
the dust and diminish with elevation and stillness. At the 
same time, we cannot forget that it is in the lower strata. 
of the atmosphere that we are compelled to live. 
THe New Gases. 
We must now return for a moment or two to Cavendish. 
Cavendish began his “ Experiments on Air” in 1777, and 
published six or seven years later. He established endio- 
metry as an exact method, absorbed the oxygen with nitric 
oxide and water, and demonstrated by analysis the apparent 
uniformity in composition of atmospheric air. He found 
