ABSTRACT
Passing over any further reference to popular or ancient usage the word element received for the first time a definition with a scientific character from Robert Boyle in the seventeenth century. His definition has been among chemists since his day. An element, according to Boyle, is a substance which resists analysis. It consists of one kind of matter, and by no known process is it possible to extract from it more than one kind of stuff. In the course of experiments on the specific heats of the elements at low temperatures between the boiling-points of liquid nitrogen and hydrogen, Sir James Dewar has observed that the mean atomic heats (at 50° Abs.) of the elements are a periodic function of the atomic weights. The importance of the periodic scheme, as arranged by Mendeléeff, deserves a little further notice in view of the influence it has had on the progress of theoretical chemistry.
