The invention of logarithms and the calculation of the earlier tables form a very striking episode in the history of exact science, and, with the exception of the _Principia_ of Newton, there is no mathematical work published in the country which has produced such important consequences, or to which so much interest attaches as to Napier's _Descriptio_. The calculation of tables of the natural trigonometrical functions may be said to have formed the work of the last half of the 16th century, and the great canon of natural sines for every 10 seconds to 15 places which had been calculated by Rheticus was published by Pitiscus only in 1613, the year before that in which the _Descriptio_ appeared. In the construction of the natural trigonometrical tables Great Britain had taken no part, and it is remarkable that the discovery of the principles and the formation of the tables that were to revolutionize or supersede all the methods of calculation then in use should have been so rapidly effected and developed in a country in which so little attention had been previously devoted to such questions. For more detailed information relating to Napier, Briggs and Vlacq, and the invention of logarithms, the reader is referred to the life of Briggs in Ward's _Lives of the Professors of Gresham College_ (London, 1740); Thomas Smith's _Vitae quorundam eruditissimorum et illustrium virorum_ (Vita Henrici Briggii) (London, 1707); Mark Napier's _Memoirs of John Napier_ already referred to, and the same author's _Naperi libri qui supersunt_ (1839); Hutton's _History_; de Morgan's article already referred to; Delambre's _Histoire de l'Astronomie moderne_; the report on mathematical tables in the _Report of the British Association_ for 1873; and the _Philosophical Magazine_ for October and December 1872 and May 1873. It may be remarked that the date usually assigned to Briggs's first visit to Napier is 1616 and not 1615 as stated above, the reason being that Napier was generally supposed to have died in 1618; but it was shown by Mark Napier that the true date is 1617.