Paper, 'Dispersion equivalents. Part I' by J H [John Hall] Gladstone Gladstone writes: 'The idea of refraction equivalents has become familiar to those who work on the borderland of optics and chemistry, and the value of that property as a means of investigating the chemical structure of compounds is becoming more and more recognised. There is a similar property, perhaps equally valuable for the same object, which has attracted little attention hitherto; I allude to the equivalent of dispersion. During the last twelve months, however, I have collated old measurements of the length of the spectrum, whether made by myself or by others, and have added many new determinations, and I am now in a position to submit some of the results to the Society.' Annotations in pencil and ink throughout. Subject: Chemistry Received 24 May 1887. Read 16 June 1887. A version of this paper was published in volume 42 of the Proceedings of the Royal Society as 'Dispersion equivalents. Part I'. 1887