is interesting to read the comments of Faraday: "This circumstance (the numerical relations between chlorin, bromin and iodin) has been made the basis of some beautiful speculations by M. Dumas, speculations which have scarcely yet assumed the consistence of a theory, and which are at the present time to be ranged among the poetic daydreams of a philosopher; to be regarded as some of the poetic illuminations of the mental horizon, which possibly may be the harbinger of a new law. . . . We seem here to have the dawning of a new light, indicative of the mutual convertibility of certain groups of elements, although under conditions which as yet are hidden from our scrutiny." In the succeeding decade we find many chemists speculating in a similar way upon the connection which seemed to subsist between the different elements.
The two chemists whose names are associated with the dawn of the Periodic Law are De Chancourtois and Newlands. De Chancourtois arranged the elements in the order of their atomic weights in a helix inscribed upon a vertical cylinder; this he called a 'telluric screw,' and although there were many inaccuracies, as a whole it approached a form in which the Periodic Law is to-day sometimes represented. The ideas of De Chancourtois were by no means free from considerable haze, as, for example, when he states that 'the properties of bodies are the properties of numbers.' This may well be interpreted in the light of the Periodic Law, which affirms that the properties of elements are functions of their atomic weights. Even the important idea of periodicity is not overlooked by De Chancourtois, but the speculations of this ingenious French engineer and geologist had practically no effect upon the chemical thought of that day; indeed, his articles were almost unnoticed and were resurrected only after they had slumbered for nearly thirty years in obscurity.
Somewhat otherwise was it with the work of Newlands, which began to appear in 1863, just a year later than that of his French contemporary. His work was, however, wholly independent of that of De Chancourtois. His first paper was chiefly concerned with the development of numerical relations between the atomic weights, following out the ideas early expressed in Döbereiner's triads. He enlarged this so as to include more than three elements in a group. For example, not only was sodium the middle member, with mean properties, of the triad, lithium, sodium, potassium; but rubidium also belonged to this group, because two of potassium plus one of lithium gives the atomic weight of rubidium. A year later he announced his law of octaves, which is generally looked upon as a forerunner of the Periodic Law. Here he arranged the elements in the order of their atomic weights and showed that "elements having consecutive numbers frequently either belong to the same group or occupy similar positions in different
