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Rh to make any statement in regard to the way in which the atoms are connected in the molecules. Yet this is just what the chemist of to-day does, and the results accomplished by working in the way referred to fully justify him. Let no one to whom the facts are unknown accuse him of indulging in useless speculation. Chemical hypotheses are for the use of chemists; and so long as they are helpful, so long as they lead to a clearer and clearer recognition of the great truths of our subject, so long as they lead us on to work, and the science grows in consequence, it is not pertinent to remark that there may possibly be a flaw somewhere. If there are flaws in chemical hypotheses, they will be recognized by chemists themselves sooner than by others. Let no one think that science has nothing to do with the realm beyond the senses. Without the aid of the imagination there could be no science. However important they are, facts alone could not constitute a science. It is necessary that the relations between these facts should be discerned, and this can not be done except by the aid of the imagination. There have been few bolder flights than those which pertain to matters of science. The greatest genius is he who sees furthest beyond the facts, and with the aid of his imagination is able to bring together into a harmonious whole those facts which seem least connected. But, it must be remembered, it is the imagination of the thoroughly trained mind, kept in subjection by profound knowledge, that leads to great results.

I have said that of late attempts have been made to learn something of the shape of molecules. Within a few months a remarkable paper, written by Prof. Wislicenus, of the University of Leipsic, has appeared, in which the actual arrangement of atoms in the molecules is seriously and brilliantly discussed. I can not even touch upon the contents of that paper. Suffice it to say that chemists generally are profoundly interested in the arguments of Wislicenus, and the subject is now under active discussion. To me it appears that the views put forward are well worthy of most serious consideration. What the outcome will be, none can predict; but, at all events, the fact is significant that chemistry has reached a stage when such a subject can be discussed.

Another subject which is coming to the front in chemistry is that which I had in mind at the beginning of this article when I said, "I accept this statement as expressing half the truth." It is unquestionably the chemist's business to tell what things are made of, but the other half of the truth is this: it is also his business to study the chemical act itself. In any given case he must not be satisfied when he has learned that when two substances, A and B, are brought together, they combine to form the new substance, A B, He must study that act of combination, and learn all he can about it. As these acts in most cases take place