Of the above-mentioned sources of the various readings found in the text of ancient authors, it should be remembered that the operation of the _first_ was confined to the short term of the author’s life; nor indeed, whatever may be the amount or importance of variations arising from _this_ source, must they go to swell the number of _corruptions_ of the text. The _second_ source of variations was indeed open during the lapse of many centuries; yet it has always been held in check by the diligent collation of copies, on the part of industrious critics, from age to age: and a large proportion of errors, arising from mere inadvertency, are either so palpable as to suggest the means of their own correction; or they are so trivial as to merit no attention, except from those who charge themselves with the responsibilities of an editor. There is, besides, reason to believe that not a few existing copies of the most celebrated authors, present a text that has passed through the process of transcription not oftener than once or twice; and that each time the copy has been executed with scrupulous exactness. Variations arising from the _third_ and _fourth_ sources, have perhaps occasioned to critics and editors more perplexity than those springing from any other cause; and yet these differences are rarely of any moment, so far as the sense of the author is concerned: they can be deemed important only when they tend to perplex the question of the date or the genuineness of a book. Corruptions of the _fifth_ class must be acknowledged materially to affect the credit and value of ancient literature, so far as there can be any reason to suspect their existence; and every diligent student of history will think the investigation of cases of this kind deserving of his utmost attention. CHAPTER III. THE DATE OF ANCIENT WORKS, INFERRED FROM THE QUOTATIONS AND REFERENCES OF CONTEMPORARY AND SUCCEEDING WRITERS. Let us now suppose, that the Greek and Latin authors are extant only in the printed editions--that is to say, that every one of the ancient manuscripts has long since perished, and that the facts that have been referred to in the preceding pages are out of our view, or unknown. Our business then would be, to collect from these works such a series of mutual references, as should both prove the identity of the works now extant with those so referred to; and also fix the relative places of the several writers in point of time.