=109.= The weakening hold of the Stoics upon the principles of their founder first becomes evident in the department of physics. Thus it is an essential part of the theory which the Stoics borrowed from Heraclitus, that as the whole universe has proceeded from the all-creative fire, so it must in due course be re-absorbed in it, this periodical re-absorption being technically known as the ‘conflagration’ (ἐκπύρωσις). On the other hand the followers of Aristotle, following dualistic principles, placed God and the universe in eternal contrast, and held both to be immortal. Ingenious controversialists now pressed the Stoics to explain how their deity exercised his providence during the periodic intervals in which the universe had no separate existence. This and like arguments had an immediate effect. BOËTHUS of Sidon, a contemporary of Chrysippus, abandoned altogether the Stoic theory on this subject[110]; ZENO of Tarsus, who had been with his father DIOSCORIDES a pupil of Chrysippus, and who succeeded him as head of the school, discreetly ‘suspended his judgment’ upon the point[111]. But whatever its theoretical embarrassments, the Stoic school continued to prosper. Zeno of Tarsus wrote but few books, but had more disciples than any other[112]; he was succeeded by SELEUCUS of the Tigris[113], and he in turn by Diogenes[114], Antipater, and Panaetius. The last of these maintained Zeno’s ‘suspense of judgment[115]’ on the question of the conflagration; but after his death the Stoics quietly returned to the older opinion. [Sidenote: Diogenes and Antipater.]