THE production of ozone by the discharge of a frictional electrical machine was originally noticed by Van Marum in 1785, but it was Schönbein in 1840 who first actually prepared it and gave it the name of “ozone,” from the Greek óζων, meaning smell. He also showed that it was much more active as an oxidising agent than ordinary oxygen. As is well known, it is produced by the slow oxidation of phosphorus, and the peculiar odour of this element is really not the odour of phosphorus, but the odour of ozone, and this can be shown to be the case by adding small quantities of substances to phosphorus, which prevent its oxidation, when the odour is no longer perceptible. It also appears to be produced in small quantities by the burning of hydrocarbons. It is likewise formed in the open country, partly by evaporation, but probably most largely by the action of ultraviolet rays from the sun. This at any rate would account for its formation in the higher regions of the atmosphere. It is formed in considerable quantities when fluorine acts upon water. If a drop of water is introduced into a tube filled with fluorine, reaction immediately ensues, and the tube becomes filled with deep blue vapour. This is ozone which has a blue colour when concentrated.