The alchemists were right. There is a philosopher's stone; but that stone is itself a compound of labour, perseverance, and genius, and the gold which it produces is the gold of true knowledge, which shall never grow dim or fade away. CHAPTER VIII. SUMMARY AND CONCLUSION. We have thus traced some of the main paths along which Chemistry has advanced since the day when, ceasing to be guided by the dreams of men who toiled with but a single idea in the midst of a world of strange and complex phenomena, she began to recognize that Nature is complex but orderly, and so began to be a branch of true knowledge. In this review we have, I think, found that the remark made at the beginning of the introductory chapter is, on the whole, a just one. That the views of the alchemists, although sometimes very noble, were "vague and fanciful" is surely borne out by the quotations from their writings given in the first chapter. This period was followed by that wherein the accurate, but necessarily somewhat narrow conception of the Lavoisierian chemistry prevailed. Founded for the most part on the careful, painstaking, and quantitative study of one phenomenon--a very wide and far-reaching phenomenon, it is true--it was impossible that the classification introduced by the father of chemical science should be broad enough to include all the discoveries of those who came after him. But although this classification had of necessity to be revised and recast, the genius of Lavoisier enunciated certain truths which have remained the common possession of every chemical system. By proving that however the forms of matter may be changed the mass remains unaltered, he for the first time made a science of chemistry possible. He defined "element" once for all, and thus swept away the fabric of dreams raised by the alchemists on the visionary foundation of _earth_, _air_, _fire_ and _water_, or of _mercury_, _sulphur_ and _salt_. By his example, he taught that weighings and measurements must be made before accurate knowledge of chemical reactions can be hoped for; and by his teaching about oxygen being _the acidifier_--although we know that this teaching was erroneous in many details--he showed the possibility of a system of classification of chemical substances being founded on the actually observed properties and composition of those substances. Lavoisier gained these most important results by concentrating his attention on a few subjects of inquiry. That chemistry might become broad it was necessary that it should first of all become narrower.