On account of the rapid decay of the radiating power of thorium emanations, it is not possible to determine its coefficients of diffusion in the same way; but special experiments show that it diffuses rapidly, and is also probably gaseous in character. T he physical properties of these emanations or gases are most remarkable. The radium emanation not only continues for long inter vals to be a source of radiation which is apparently similar in character to easily absorbed Röntgen rays, but in some way manufactures from itself a positively charged substance, which travels to the negative electrode and becomes a source of secondary radioactivity. [Footnote 1: Wiener Akad., 1871.] TRANSCRIBER'S NOTES This article was published in the Proceedings And Transactions Of The Royal Society Of Canada, Second Series, Volume VII, in the Meeting of May, pp. 21-25, 1901.