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‎Condensation of Water Vapour in the Presence of Dust-free Air and other Gases. Communicated by J.J. Thomson. Received March 15, - Read April 8, 1897.‎

‎(London, Harrison and Sons, 1897). 4to. No wrappers as extracted from ""Philosophical Transactions"" Year 1897, Volume 189 - Series A. - Pp. 265-307. Clean fine. Textillustrations, depicting Wilson's famous apparatus‎

‎First printing of this groundbreaking paper in which Wilson describes the invention which made it possible to view the track of a single atomic projectile or electron. The invenvention of the ""Dust-Chamber"" made it possible for J.J. Thomson in 1897 to calculate the charge of the electron, and thereby finding its mass, since the ratio between the two was known. In most cases it was found that the track of the particle is a straight, or nearly straight line.""C.T.R. Wilson had been developing his cloud-chamber, which was to provide the most powerfull of all methods of investigation in atomic physics. In moist air, if a certain degree of supersaturation is exceeded this can be secured by a sudden expansion of the air) condensation takes place on dust-nuclei, when any are present: if by preliminary operations condensation is made to take place on the dust-nuclei, and the resulting droplets are allowed to settle, the air in the chamber is thereby freed from dust. If now X-rays or radiation from a radioactive substance are passed into the chamber, and if the degree of supersaturation is sufficient, condensation again takes place: this is due to the production of ions by the radiation. Thus the tracks of ionising radiations can be made visible by the sudden expansion of a moist gas, each ion becoming the centre of a visible globule of water. Wilson showed that the ions produced by uranium radiation were identical with those produced by X-rays."" (Whittaker in ""A History of the Theories of Aether & Electricity"" II:p.4).‎