Little did Dalton dream that the “atomic weight” of the elements is equivalent to the number of _electrons_ in each atom of a given substance![29] Or that the atomic _number_ of an element, arranged (successively) in the order of their atomic _weights_, from 1 (hydrogen) to 92 (uranium), is an index to the number of positive electrical charges on the atomic nucleus, around which revolve in “planetary orbits” an equivalent number of negatively charged _electrons_--the real building-stones of the Universe. FOOTNOTES: [Footnote 28: _Nicholson’s Journal_, 29, 147, 1811.] [Footnote 29: On this point, see Lodge, Sir Oliver, “Within the Atom,” _Scientific American_, November, 1923.] =TRANSCRIBER’S NOTES= Simple typographical errors have been silently corrected; unbalanced quotation marks were remedied when the change was obvious, and otherwise left unbalanced. Punctuation, hyphenation, spelling and ligatures were made consistent when a predominant preference was found in the original book; otherwise they were not changed. The verses of the Invictus poem have been left as they are in the printed version. A Table of Contents has been added.