From the time of the Ptolemies the scientific spirit of the Alexandrian school declined; for though such mathematicians as Theodosius, whose work on Spherical Geometry was greatly valued by the Arab geometers; and Pappus, whose mathematical collections, in eight books, still for the most part remain; and Theon, doubly celebrated for his geometrical attainments, and as being the father of the unfortunate Hypatia, A.D. 415, lived in the next three centuries, they were not men like their great predecessors. That mental strength which gives birth to original discovery had passed away. The commentator had succeeded to the philosopher. No new development illustrated the physical sciences; they were destined long to remain stationary. Mechanics could boast of no trophy like the proposition of Archimedes on the equilibrium of the lever; no new and exact ideas like those of the same great man on statical and hydrostatical pressure; no novel and clear views like those developed in his treatise on floating bodies; no mechanical invention like the first of all steam-engines--that of Hero. Natural Philosophy had come to a stop. Its great, and hitherto successfully cultivated department, Astronomy, exhibited no farther advance. Men were content with what had been done, and continued to amuse themselves with reconciling the celestial phenomena to a combination of equable circular motions. To what are we to attribute this pause? Something had occurred to enervate the spirit of science. A gloom had settled on the Museum. [Sidenote: Causes of that decline.]