Page:Popular Science Monthly Volume 27.djvu/554

536 progress of those branches of natural knowledge the advancement of which is the object of the vast collections gathered here. It has given me much pleasure to learn that the memorial has received so much support in foreign countries that it may be regarded as cosmopolitan rather than as simply national; while the fact that persons of every condition of life have contributed to it affords remarkable evidence of the popular interest in the discussion of scientific problems. A memorial to which all nations and all classes of society have contributed can not be more fitly lodged than in our Museum, which, though national, is open to all the world, and the resources of which are at the disposal of every student of Nature, whatever his condition or his country, who enters our doors.—Nature.



E had in the earlier ages of mankind a rough and a polished stone age, a bronze age, and an age of iron, each distinguished by the character of the material that was predominantly used by men for their weapons and tools, and have now added to those ages one of steel. In a similar manner we are now entering upon a revival of the bronze age, in which that substance in its varieties is to be put through stages of improvement like those that iron and steel have undergone. Many varieties of bronze have been produced within the last few years that possess features strongly distinguishing them from the ancient alloys, and some very remarkable qualities as compared with them, in view of which they are frequently used in place of even iron and steel, The bronzes of the ancients were composed of copper and tin, as is also what is now regarded as bronze pure and simple, mixed in proportions varying according to the purpose for which the compound is intended. Other substances, however, are often added, without un-classifying the product, which is still called bronze, provided copper and tin are the chief constituents. Among these substances are zinc, lead, phosphorus, manganese, silicium, iron, nickel, arsenic, antimony, and sulphur. It is the addition of certain proportions of one or other of such substances that constitutes the modern development of bronze manufacture, and which has given us some of the most useful and at the same time some of the most remarkable alloys known. These comprise no fewer than eleven distinct products, all of which find their uses in connection with the practice of engineering. They are: phosphor-bronze, silicium-bronze, manganese-bronze, delta-metal, 