The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.

If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity.

We must expect the discovery of many as yet unknown elements-for example, elements analogous to aluminum and silicon- whose atomic weight would be between 65 and 75.

Certain characteristic properties of elements can be foretold from their atomic weights.

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It is the function of science to discover the existence of a general reign of order in nature and to find the causes governing this order. And this refers in equal measure to the relations of man - social and political - and to the entire universe as a whole.

No law of nature, however general, has been established all at once; its recognition has always been preceded by many presentiments.