In 1623 appeared the poet's fourth publication, entitled "Flowers of Sion: By William Drummond of Hawthornedenne: to which is adjoyned his Cypresse Grove". From 1625 till 1630 Drummond was probably for the most part engaged in travelling on the Continent. On 29 September 1626 he received a sixteen patents for diverse devices, mainly military. These included Glasses of Archimedes which could set ships afire at sea and an early form of machine gun "in which a number of musket barrels are fastened together in such a manner as to allow one man to take the place of a hundred musketeers in battle. However, there is no evidence that he actually produced any of these devices. In 1627, however, he seems to have been home for a short time, as, in that year, he appears in the entirely new character of the holder of a patent for the construction of military machines, entitled "Litera Magistri Gulielmi Drummond de Fabrica Machinarum Militarium, Anno 1627". The same year, 1627, is the date of Drummond's munificent gift (referred to above) of about 500 volumes to the library of the University of Edinburgh.