DEVELOPMENT OF METEOROLOGY—ABBE. 291 
cosmical physics, the new ideas that we get from the laboratory study 
of chemistry, electricity, hydrodynamics, and radiation, the broaden- 
ing of our field of observation by the use of wireless telegraphy, all 
conspire toward the better establishment of our science and conse- 
quently the perfecting of the daily predictions. 
ELEMENTARY METEOROLOGY. 
In every branch of human activity we begin with the simplest ideas 
and easiest actions, and then progress to the most complex combina- 
ticns and most difficult constructions, eventually arriving at abstrac- 
tions of whose essence we know nothing, but whose effects are observ- 
able and measurable. This statement apples to all branches of 
science, and meteorology is no exception. We begin with the direct 
tesimony of the senses, then we recognize the abstract idea that force 
must pervade nature and must be the foundation of all the phenomena 
that we have apprehended by means of our five senses. 
The simplest atmospheric phenomena were first observed, and these 
stimulated the earliest philosophers of classical antiquity. Until 
most recent times meteorology was not advanced by the work of pro- 
fessional meteorologists so much as by occasional contributions from 
those whom we ordinarily speak of as astronomers, geographers, 
physicists, chemists, but who in earlier times were known as philoso- 
phers. 
To the astronomers we owe certain fundatmental facts, namely, 
that the earth is a sphere, that it rotates on its axis and revolves about 
the sun and that its axis is inclined to the ecliptic. To establish these 
few simple points required two thousand years—from the days of 
Eratosthenes, born 276 B. C., at Alexandria, down to the time of 
Copernicus, who died in 1543, and of Galileo, who died in 1642. 
To the students of optics we owe the explanation of the twilight, 
first correctly given by the Arab, Alhazen, who lived in Spain in the 
eleventh century, but who may have drawn much of his knowledge 
from earlier Alexandrian Greek manuscripts that are now unknown. 
But even he knew nothing of the ultimate cause of the refractive 
power of the atmosphere; he attributed it to the transparency of the 
air rather than to its density; whereas Kleomedes, A. D. 50, seemed 
to understand that it is the density of the medium that principally 
determines the amount of refraction. 
The rainbow and its supplementary bows and halos in general were 
observed more or less accurately in the earliest ages and are mentioned 
by Aristotle, who knew that they depended in some way upon the 
position of the sun. The first steps in the proper explanation of the 
rainbow were taken by Vitellio, who began by observing carefully the 
rainbows formed in the spray of the waterfall at Viterbo; his work 
