ere is one essential quality in physical conceptions, which was
entirely wanting in those of Aristotle and his followers--a capability
of being placed as coherent pictures before the mind. The Germans
express the act of picturing by the word vorstellen, and the picture
they call a Vorstellung. We have no word in English which comes
nearer to our requirements than Imagination; and, taken with its
proper limitations, the word answers very well. But it is tainted by
its associations, and therefore objectionable to some minds. Compare,
with reference to this capacity of mental presentation, the case of
the Aristotelian, who refers the ascent of water in a pump to Nature's
abhorrence of a vacuum, with that of Pascal when he proposed to solve
the question of atmospheric pressure by the ascent of the Puy de Dome.
In the one case the terms of the explanation refuse to fall into place
as a physical image; in the other the image is distinct, the descent
and rise of the barometer being clearly figured beforehand as the
balancing of two varying and opposing pressures.

3.

During the drought of the Middle Ages in Christendom, the Arabian
intellect, as forcibly shown by Draper, was active. With the
intrusion of the Moors into Spain, order, learning, and refinement
took the place of their opposites. When smitten with disease, the
Christian peasant resorted to a shrine, the Moorish one to an
instructed physician. The Arabs encouraged translations from the
Greek philosophers, but not from the Greek poets. They turned in
disgust 'from the lewdness of our classical mythology, and denounced
as an unpardonable blasphemy all connection between the impure
Olympian Jove and the Most High God.' Draper traces still farther
than Whewell the Arab elements in our scientific terms. He gives
examples of what Arabian men of science accomplished, dwelling
particularly on Alhazen, who was the first to correct the Platonic
notion that rays of light are emitted by the eye. Alhazen discovered
atmospheric refraction, and showed that we see the sun and the moon
after they have set. He explained the enlargement of the sun and
moon, and the shortening of the vertical diameters of both these
bodies when near the horizon. He was aware that the atmosphere
decreases in density with increase of elevation, and actually fixed
its height at 58.5 miles. In the 'Book of the Balance of Wisdom,' he
sets forth the connection between the weight of the atmos