To bar controversies and partisan discussion as to the relative merits of different discoverers and inventors, concerning which authorities are at variance, it has been thought best to quote all of the weightiest known authorities under the respective heads and dates of the several claimants. To the would-be historian and to the delving student, this will certainly appear the better course. A case in point, and it is no uncommon one, attaches to the invention of the mariner’s compass, where that instrument and its original employment in navigation are credited with equal assurance to China, Iceland, France, England and Italy, by equally eminent historians and scientists. And, as nearly all, except the very earliest, discoveries of any high importance have already been traced to their respective origins by many authors, additional data have been gathered and quoted wherever such data seemed deserving of more than the ordinary notices previously accorded them in print, or where the peculiar nature of the discovery, or the identity of its author, merited authentication to preclude doubt or controversy. The unusual number of cumulative references purposely given throughout many entries (the most important of which were originally set in italics) cannot be seriously objected to, as they afford ready means for making searches through different accessible channels, covering various phases of a subject, and they facilitate the verification of all extracts and of all quoted passages. They likewise effectually offset the likelihood of misprints necessarily attaching to many of the authorities which are cited from, and which often can be found solely in, rare early publications or in more or less unintelligible manuscripts. Only those who have had to make important searches through such can appreciate the difficulties which continually beset the investigator. Many of the older serials likewise prove quite unreliable and disappointing, either through wrong pagination or irregular and sometimes conflicting dates of publication, as well as through the rearrangement or redistribution of parts or series, at various periods and in different volumes. This is the case, more particularly, with “Le Journal des Savants” and with “The Philosophical Transactions,” as it is also with many technical serial publications of various countries which are referred to in the following pages.