on the library tables. Here is the first model of Davy's safety-lamp; there a chronometer which aided Cook in his famous voyage round the world. This is Wollaston's celebrated "Thimble Battery." It will slip readily into the pocket, yet he jestingly showed it to a visitor as "his entire laboratory." That is a model of the double-decked boat made by Sir William Petty, and there beyond is a specimen of almost, if not quite, the first radiometer devised by Sir William Crookes. As one stands in the presence of all these priceless relics, so vividly do the traditions of more than two centuries of science come to mind that one seems almost to have lived through them. One recalls, as if it were a personal recollection, the founding of the Royal Society itself in 1662, and the extraordinary scenes which the society witnessed during the years of its adolescence. As one views the mementos of Boyle and Newton, one seems to be living in the close of the seventeenth century. It is a troublous time in England. Revolution has followed revolution. Commonwealth has supplanted monarchy and monarchy commonwealth. At last the "glorious revolution" of 1688 has placed a secure monarch on the throne. But now one external war follows another, and the new king, William of Orange, is leading the "Grand Alliance" against the French despot Louis XIV. There is war everywhere in Europe, and the treaty of Ryswick, in 1697, is but the preparation for the war of the Spanish Alliance, which will usher in the new century. But amid all this political turmoil the march of scientific discovery has gone serenely on; or, if not serenely, then steadily, and perhaps as serenely as could be hoped. Boyle has discovered the law of the elasticity of gases and a host of minor things. Robert Hooke is on the track of many marvels. But all else pales before the fact that Newton has just given to the world his marvellous law of gravitation, which has been published, with authority of the Royal Society, through the financial aid of Halley. The brilliant but erratic Hooke lias contested the priority of discovery and strenuously claimed a share in it. Halley eventually urges Newton to consider Hooke's claim in some of the details, and Newton yields to the extent of admitting that the great fact of gravitational force varying inversely as the square of the distance had been independently discovered by Hooke; but he includes also Halley himself and Sir Christopher Wren, along with Hooke, as equally independent discoverers of the same principle. To the twentieth-century consciousness it seems odd to hear Wren thus named as a scientific discoverer; but in truth the builder of St. Paul's began life as a professor of astronomy at Gresham College, and was the immediate predecessor of Newton himself in the presidential chair of the Royal Society. Now, at the very close of the seventeenth century, Boyle is recently dead, but Hooke, Wren, Halley, and Newton still survive: