The treatise of Albategnius on "The Science of the Stars" is spoken of by Laplace with respect; he also draws attention to an important fragment of Ibn-Junis, the astronomer of Hakem, the Khalif of Egypt, A.D.

1000, as containing a long series of observations from the time of Almansor, of eclipses, equinoxes, solstices, conjunctions of planets, occultations of stars--observations which have cast much light on the great variations of the system of the world.

The Arabian astronomers also devoted themselves to the construction and perfection of astronomical instruments, to the measurement of time by clocks of various kinds, by clepsydras and sun-dials.

They were the first to introduce, for this purpose, the use of the pendulum.
In the experimental sciences, they originated chemistry; they discovered some of its most important reagents--sulphuric acid, nitric acid, alcohol.

They applied that science in the practice of medicine, being the first to publish pharmacopoeias or dispensatories, and to include in them mineral preparations.