prophesied the discovery of elements then unknown which would fill these gaps. Not only this, but he boldly ventured to describe some of these unknown elements in detail. At first no one was inclined to give serious consideration to the predictions; certainly no one dreamed that they would soon prove to be among the most brilliant predictions ever recorded in the annals of science. Within a few years all three of the elements predicted by Mendelejeff were discovered—the last one about two years ago. The first one was discovered in France, and was hence called gallium; the second, discovered in Norway, is known as scandium; and the third, recently discovered in Germany, is the baby element germanium. The descriptions given by Mendelejeff, eighteen years ago, are found to agree marvelously well with the facts. These discoveries have directed the attention of all chemists to the periodic law, and have lent a new interest to the discovery of new elements. There are undoubtedly others still undiscovered. Let us hope that the next one may come to light in the New World, and that we may thus have our own particular element, as France and Norway and Germany have theirs.
It is obvious from what I have already said that, to tell what things are made of, is not so simple a matter as it might at first appear. The best answer we can give, in any case, is lamentably incomplete. But there is another side to the subject, one of fascinating interest. Let me endeavor to illustrate this by means of another example. It has long been known that there are two substances, called respectively glucose and levulose, which are made of the same elements, viz., carbon, hydrogen, and oxygen, in exactly the same proportion by weight. Notwithstanding the fact that these two substances have exactly the same composition, they have markedly different properties. Chemistry abounds in similar examples. To account for these facts, chemists suppose that the parts of which the two substances are made up are arranged differently. An immense amount of work has been done during the past half-century with the object of reaching conclusions concerning what is called the constitution of chemical compounds, and the results reached in this field have been brilliant in the highest degree. By methods of the most refined character the chemist of to-day is enabled to enter into the innermost recesses of compounds, and trace out the connections which exist between the constituent parts. Many of the most complex compounds found in nature have thus been studied, their constitution determined, and methods have in many cases been devised by which the substances found in nature can be built up in the chemical laboratory without the intervention of the life process. Among recent achievements in this direction I may mention indigo. This is remarkably complex, and for a long time it had baffled all
