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achieve what would have been, if not impossible, at any rate far more difficult for one alone to accomplish. From this time onward they were in almost daily intercourse, either personally or by letter, and how voluminous, interesting and intimate their literary relations were can be seen from the four volumes of their letters to one another, which were published a few years ago in Germany by Bebel and Bernstein. For the most part, Marx devoted himself to the study and investigation of the more theoretical side of their work, whilst Engels chiefly devoted his energies to the practical application of their theoretical deductions, and particularly, later on, to the propaganda of their ideas and to polemics with their opponents. But we have it on the authority of Engels himself that scarcely a word that either wrote or a policy that they promulgated but was discussed between them first.
THEIR MATERIALIST DIALECTICS.
Their first scientific work was a complete break with the contemporary school of German philosophy. We have already mentioned that Marx, when still studying in Berlin, had joined the school of Young Hegelians. Marx had made himself thoroughly master of the Hegelian philosophy, without, however, becoming a slavish imitator or disciple. He extracted from it all that was revolutionary and useful for the study and interpretation of history. The Hegelian philosophy proposes, as a law of progress, the continuous transformation and upsetting of existing conditions and the continuous growth of new oppositions and the overcoming of existing ones. It puts it down as a law that the germ of the new exists in the old, that as this germ develops, so at first the difference between the two is merely quantitative, but when the quantitative difference has reached a certain stage, there is a break between the two and the difference becomes qualitative. This law is true throughout organic and inorganic nature, and it is perhaps well worth one's while to stop to illustrate it by a few examples. In chemistry, we know of a number of series of carbon compounds, only differing one from the other by the number of carbon and hydrogen atoms they contain. Thus if we take marsh gas we may represent it by CH4. If we add to this under whatever conditions,
