They perceived that it can never be advanced by mere speculation; its only sure progress is by the practical interrogation of Nature.

The essential characteristics of their method are experiment and observation.

Geometry and the mathematical sciences they looked upon as instruments of reasoning.

In their numerous writings on mechanics, hydrostatics, optics, it is interesting to remark that the solution of a problem is always obtained by performing an experiment, or by an instrumental observation.

It was this that made them the originators of chemistry, that led them to the invention of all kinds of apparatus for distillation, sublimation, fusion, filtration, etc.; that in astronomy caused them to appeal to divided instruments, as quadrants and astrolabes; in chemistry, to employ the balance, the theory of which they were perfectly familiar with; to construct tables of specific gravities and astronomical tables, as those of Bagdad, Spain, Samarcand; that produced their great improvements in geometry, trigonometry, the invention of algebra, and the adoption of the Indian numeration in arithmetic.