J. D. EVERETT, M.A., D.C.L., F.R.S., F.R.S.E., PROFESSOR OF NATURAL PHILOSOPHY IN QUEEN'S COLLEGE, belfast. [The right of translation and reproduction is reserved.] PREFACE. THIS work, in its original form, was published by the Physical Society of London, in 1875, as "Illustrations of the C.G.S. System of Units." A greatly enlarged edition was issued in 1879 by the present publishers, and the title was changed to "Units and Physical Constants," the letters "C.G.S." being suppressed from an idea that their strangeness would unfavourably influence the sale. This new title was retained in the "second edition" issued in 1886. The C.G.S. units having now become the accepted standards of reference throughout the scientific world, there is no longer any reason for suppressing the name. In the present edition they are accordingly restored to their place in the title, which is thus brought into closer agreement with the contents of the book. The German edition, which was announced in our last preface as about to appear, was published at Leipsic in 1888 by Ambrosius Barth. It is a close translation as regards the portions relating to units, but contains large changes in the experimental data, some years having been devoted to this portion of the undertaking after the original manuscript had been completed. The present edition has been closely compared with the German |