"The article "Chemistry," which was 261 pages long in the 3rd, written by James Tytler, and had been re-written in that edition's supplement as a 191-page treatise by Thomas Thomson, appears in the 4th edition as an entirely new 358-page article, which, according to the preface to the 5th edition, was authored by Millar himself.The new treatise was necessary because the copyright to the supplement to the 3rd, which included Thomson's excellent treatise, was not owned by Britannica.