ADDRESS. 19 
ventors are able to advance the arts. In illustration of how slowly at 
first and how rapidly afterwards science and its applications arise, I will 
take only two out of thousands of examples which lie ready to my hand. 
One of the most familiar instances is air, for that surely should have been 
soon understood if man’s unaided senses are sufficient for knowledge. Air 
has been under the notice of mankind eyer since the first man drew his 
first breath. It meets him at every turn ; it fans him with gentle breezes, 
and it buffets him with storms. And yet it is certain that this familiar 
object—air—is very imperfectly understood up to the present time. We 
now know by recent researches that air can be liquefied by pressure and 
cold; but as a child still looks upon air as nothing, so did man in his 
early state. A vessel filled with air was deemed to be empty. But man, 
as soon as he began to speculate, felt the importance of air, and deemed 
it to be a soul of the world upon which the respiration of man and the 
god-like quality of fire depended. Yet a really intelligent conception of 
these two essential conditions to man’s existence—respiration and com- 
bustion—was not formed till about a century ago (1775). No doubt long 
before that time there had been abundant speculations regarding air. 
Anaximenes, 548 years before Christ, and Diogenes of Apollonia, a century 
later, studied the properties of air so far as their senses would allow them ; 
so, in fact, did Aristotle. Actnal scientific experiments were made on air 
about the year 1100 by a remarkable Saracen, Alhazen, who ascertained 
important truths which enabled Galileo, Torricelli, Otto de Guericke, and 
others at a later period to discover laws leading to important practical 
applications. Still there was no intelligent conception as to the compo- 
sition of air until Priestley in 1774 repeated, with the light of science, an 
empirical observation which Eck de Sulbach had made three hundred 
years before upon the union of mercury with an ingredient of air and the 
decomposition of this compound by heat. This experiment now proved 
that the active element in air is oxygen. From that date our knowledge, 
derived from an intelligent questioning of air by direct experiments, has 
gone on by leaps and bounds. The air, which mainly consists of nitrogen 
and oxygen, is now known to contain carbonic acid, ammonia, nitric acid, 
ozone, besides hosts of living organisms which have a vast influence for 
good or evil in the economy of the world. These micro-organisms, the 
latest contribution to our knowledge of air, perform great analytical 
functions in organic nature, and are the means of converting much of its 
potential energy into actualenergy. Through their action on dead matter 
the mutual dependence of plants and animals is secured, so that the air 
becomes at once the grave of organic death and the cradle of organic life. 
No doubt the ancients suspected this without being able to prove the de- 
pendence. Euripides seems to have seen it deductively when he describes 
the results of decay :— ; 
Then that which springs from earth, to earth returns, 
And that which draws its being from the sky 
Rises again up to the skyey height 
