Next, taking out the gold, he put in the silver, which, though it weighed the same, yet, being larger, made the water rise higher; and this height he also marked. Lastly, he took out the silver and put in the crown. Now if the crown had been pure gold, the water would have risen only up to the mark of the gold, but it rose higher, and stood between the gold and silver marks, showing that silver had been mixed with it, making it more bulky; and by calculating how much water was displaced, Archimedes could estimate roughly how much silver had been added. This was the first attempt to measure the _specific gravity_ of different substances; that is, the weight of any particular substance compared to an equal bulk of some other substance taken as a standard. In weighing solids or liquids, water is the usual standard. * * * * * =How this Solid Earth keeps Changing.=--The student of history reads of the great sea-fight which King Edward III. fought with the French off Sluys; how in those days the merchant vessels came up to the walls of that flourishing sea-port by every tide; and how, a century later, a Portuguese fleet conveyed Isabella from Lisbon, and an English fleet brought Margaret of York from the Thames, to marry successive Dukes of Burgundy at the port of Sluys. In our time, if a modern traveller drives twelve miles out of Bruges, across the Dutch frontier, he will find a small agricultural town, surrounded by corn fields and meadows and clumps of trees, whence the sea is not in sight from the top of the town-hall steeple. This is Sluys. Once more. We turn to the great Baie du Mont Saint Michel, between Normandy and Brittany. In Roman authors we read of the vast forest called "Setiacum Nemus," in the centre of which an isolated rock arose, surmounted by a temple of Jupiter, once a college of Druidesses. Now the same rock, with its glorious pile dedicated to St. Michael, is surrounded by the sea at high tides. The story of this transformation is even more striking than that of Sluys, and its adequate narration justly earned for M. Manet the gold medal of the French Geographical Society in 1828.