stances carton, oxygen, and calcium made of? It is true we call them elements or simple substances, meaning by that substances which can not be converted into anything simpler. No matter what influences the so-called elements are subjected to, they can not at present be decomposed. When, therefore, a chemist, after examining any complex substance, is able to say what simple substances are in it, he tells what it is made of. But, I repeat, is his statement final? Is there nothing more to learn? Plainly the great questions still remain to be answered: What is an element? Are the forms of matter which we call elements absolutely independent of each other, or are they not in turn composed of still subtler forms of matter which we may hope to discover in the future?
While it is impossible to answer these questions at present, some discoveries have been made within the past few years which have a direct bearing upon them. It has been shown by a Russian chemist, Mendelejeff, and at the same time by a German, Lothar Meyer, that the elements are related in a very remarkable way, so closely that it is possible to arrange them all in one table, in which they form parts of a general system. The law governing the variations in properties of the elements is known as the periodic law. The limits of this article will not permit any detailed explanation of this remarkable law. The main point that I wish to emphasize is, that these so-called elements are shown to be related to one another, and it seems impossible, in the light of these facts, to believe that they are distinct forms of matter. It seems much more probable that they are in turn composed of subtler elements, and it has been pointed out that all the substances which we now call elements, of which there are about seventy, can be conceived to be made of two fundamental elements combined in different proportions. There does not, however, appear to be any immediate prospect of discovering these fundamental substances, though we can not, of course, tell what a day may bring forth. While the prospect in this direction is not promising, it appears clear that there are other elements of the same order as those now known yet to be discovered. When Mendelejeff first arranged the known elements in his table, he found that the table was not complete, and it became necessary to leave certain places vacant in order to secure a perfectly systematic arrangement. It was as if an incomplete skeleton of some great animal were found. On putting the parts together, the finder would discover that something is wanting to complete the whole, but nevertheless he would recognize the relations between the parts before him. He would also be able to tell what the general properties of the missing parts must be. So here, the discoverer of the periodic law recognized that the system was incomplete. He pointed out the gaps, and
