From this time the progress of organic chemistry became rapid. Dumas continued the researches upon ethers which he had commenced at Geneva, and by the year 1829 or so he had established the relations which exist between ethers and alcohols on the one hand, and ethers and acids on the other. This research, a description of the details of which I cannot introduce here as it would involve the use of many technical terms and assume the possession by the reader of much technical knowledge, was followed by others, whereby Dumas established the existence of a series of compounds all possessed of the chemical properties of alcohol, all containing carbon, hydrogen and oxygen, but differing from one another by a constant amount of carbon and hydrogen. This discovery of a series of alcohols, distinguished by the possession of certain definite properties whereby they were marked off from all other so-called organic compounds, was as the appearance of a landmark to the traveller in a country where he is without a guide. The introduction of the comparative method of study into organic chemistry--the method, that is, which bases classification on a comparison of large groups of compounds, and which seeks to gather together those substances which are like and to separate those which are unlike--soon began to bear fruit. This method suggested to the experimenter new points of view from which to regard groups of bodies; analogies which were hidden when a few substances only were considered, became prominent as the range of view was widened. What the gentle Elia calls "fragments and scattered pieces of truth," "hints and glimpses, germs, and crude essays at a system," became important. There was work to be done, not only by the master spirits who, looking at things from a central position of vantage, saw the relative importance of the various detailed facts, but also by those who could only "beat up a little game peradventure, and leave it to knottier heads, more robust constitutions, to run it down." Twenty years before the time of which we are now speaking Davy had decomposed the alkalis potash and soda; as he found these substances to be metallic oxides, he thought it very probable that the other well-known alkali, ammonia, would also turn out to be the oxide of a metal. By the electrolysis of salts formed by the action of ammonia on acids, using mercury as one of the poles of the battery, Davy obtained a strange-looking spongy substance which he was inclined to regard as an alloy of the metallic base of ammonia with mercury. From the results of experiments by himself and others, Davy adopted a view of this alloy which regarded it as containing a _compound radicle_, or group of elementary atoms which in certain definite chemical changes behaved like a single elementary atom. To this compound radicle he gave the name of _ammonium_.