In 1715, the famous astronomer Edmund Halley published a paper entitled “A Short Account of the Saltness of the Ocean.... With a Proposal by Help Thereof to Discover the Age of the World.” No definite progress was made, however, until 1899, when Joly pointed out that of the many elements which enter into the composition of salt water, sodium alone tends to accumulate. All the others are sooner or later rejected, associating themselves with the detrital sediments, or forming chemical or organic sediments by their ultimate precipitation. He accordingly used sodium as the index of the age of the oceans. He assumed that the annual increase of sodium has been more or less constant, being added to every year by the quantity washed into the ocean by the rivers. How long a period of time would it require to reach its present degree of saltness? Taking all the oceans as one, the volume of the ocean is approximately 320,000,000 cubic miles. Its density (according to Murray) is 1.026. On the basis of these figures, Joly, and after him Sollas and others, calculated that it would require from 80 to 150 million years for the present degree of salinity to be reached. Ninety or a hundred million years would be a fair estimate. Indirectly therefore, the study of the salinity of the oceans has thrown light upon the age of our earth, and its chemical constitution throughout geological ages. THE NEWER CHEMISTRY It will be seen, therefore, that chemistry has not only proved of the utmost practical value to mankind, but that it has been instrumental in solving some of the greatest enigmas confronting the mind of man, and in settling some philosophical and even theological questions. (The age of the earth, the composition and habitability of distant stars, etc.) Attempts have been made to account for life itself along purely physico-chemical lines. And all this was attempted--and in part even rendered possible--before the ultimate constitution of matter was known! During the present generation, an entirely new light has been thrown upon this central problem, and the ideas of centuries have been discarded. Let us trace the final steps of research in this direction, and see how the latest findings of modern science have thrown light upon the world-old problem of the ultimate constitution of matter. RADIO-ACTIVITY