3. Cicero’s name may also occur to us here—although he certainly is but a troubled spring—since he undoubtedly gives us much information; yet because he was lacking in philosophic spirit, he understood Philosophy rather as if it were a matter of history merely. He does not seem to have himself studied its first sources, and even avows that, for instance, he never understood Heraclitus; and because this old and deep philosophy did not interest him, he did not give himself the trouble to study it. His information bears principally on later philosophers—the Stoics, Epicureans, the new Academy, and the Peripatetics. He saw what was ancient through their medium, and, generally speaking, through a medium of reasoning and not of speculation. 4. Sextus Empiricus, a later sceptic, has importance through his writings, _Hypotyposes Pyrrhonicæ_ and _adversus Mathematicos_. Because, as a sceptic, he both combated the dogmatic philosophy and also adduced other philosophers as testifying to scepticism (so that the greater part of his writings is filled with the tenets of other philosophers), he is the most abundant source we have for the history of ancient philosophy, and he has retained for our use many valuable fragments. 5. The book of Diogenes Laertius (_De vitis_, &c., Philoss. lib. x., ed. Meibom. c. notis Menagii, Amstel. 1692) is an important compilation, and yet it brings forward copious evidence without much discrimination. A philosophic spirit cannot be ascribed to it; it rambles about amongst bad anecdotes extraneous to the matter in hand. For the lives of philosophers, and here and there for their tenets, it is useful. 6. Finally, we must speak of Simplicius, a later Greek, from Cilicia, living under Justinian, in the middle of the sixth century. He is the most learned and acute of the Greek commentators of Aristotle, and of his writings there is much still unpublished: to him we certainly owe our thanks.