stulating--have been shown to be billions
of times more numerous than any larger cosmic bodies of which we have
cognizance--so widely does the existing universe differ from man's
preconceived notions as to what it should be.

Thus also the "miracle" of the falling stone, against which the
scientific scepticism of yesterday presented "an evil heart of
unbelief," turns out to be the most natural phenomena, inasmuch as it is
repeated in our atmosphere some millions of times each day.

THE AURORA BOREALIS

If fire-balls were thought miraculous and portentous in days of yore,
what interpretation must needs have been put upon that vastly more
picturesque phenomenon, the aurora? "Through all the city," says the
Book of Maccabees, "for the space of almost forty days, there were seen
horsemen running in the air, in cloth of gold, armed with lances, like
a band of soldiers: and troops of horsemen in array encountering and
running one against another, with shaking of shields and multitude of
pikes, and drawing of swords, and casting of darts, and glittering of
golden ornaments and harness." Dire omens these; and hardly less ominous
the aurora seemed to all succeeding generations that observed it down
well into the eighteenth century--as witness the popular excitement in
England in 1716 over the brilliant aurora of that year, which became
famous through Halley's description.

But after 1752, when Franklin dethroned the lightning, all spectacular
meteors came to be regarded as natural phenomena, the aurora among the
rest. Franklin explained the aurora--which was seen commonly enough in
the eighteenth century, though only recorded once in the seventeenth--as
due to the accumulation of electricity on the surface of polar snows,
and its discharge to the equator through the upper atmosphere. Erasmus
Darwin suggested that the luminosity might be due to the ignition of
hydrogen, which was supposed by many philosophers to form the upper
atmosphere. Dalton, who first measured the height of the aurora,
estimating it at about one hundred miles, thought the phenomenon due
to magnetism acting on ferruginous particles in the air, and his
explanation was perhaps the most popular one at the beginning of the
last century.

Since then a multitude of observers have studied the aurora, but the
scientific grasp has found it as elusive in fact as it seems to casual
observation, and its exact nature is as undetermined to-day as it was a
hundred y