John Alexander Reina Newlands (November 26, 1838 - July 29, 1898) was an English analytical chemist who prepared in 1863 the first periodic table of the elements arranged in order of relative atomic masses, and pointed out in 1865 the 'law of octaves' whereby every eighth element has similar properties. He was ridiculed at the time, but five years later Russian chemist Dmitri Mendeleev published a more developed form of the table, also based on atomic masses, which forms the basis of the one used today (arranged by atomic number).

Newlands was born in London and studied there at the Royal College of Chemistry. In 1860 he served as a volunteer with Giuseppe Garibaldi in his campaign to unify Italy (Newlands was of Italian descent on his mother's side). He set up in practice as an analytical chemist in 1864, and in 1868 became chief chemist in a sugar refinery, where he introduced a number of improvements in processing. Later he left the refinery and again set up as an analyst.

Like many of his contemporaries, Newlands first used the terms 'equivalent weight' and 'atomic weight' without any distinction in meaning, and in his first paper in 1863 he used the values accepted by his predecessors. The incompleteness of a table he drew up 1864 he attributed to the possible existence of additional, undiscovered elements. For example, he predicted the existence of germanium.