THIS book, to quote from the preface, consists “of a careful compilation of the more material facts needed for an elementary understanding of radio-active phenomena, especially in relation to therapeutic and kindred progress,” and the author's aim has been “to steer a middle course between the popular and the scientific literature of the subject, avoiding over-technicality, on the one hand, and on the other, that looseness of which the popular treatment of a scientific matter is peculiarly susceptible.” On the whole the book seems fairly well fitted to fulfil its object. The author has successfully avoided over-technicality, but has not been entirely successful in retaining accuracy. In discussing the energy of radium, the view appears to be taken that because the radiations escaping are limited to a thin layer beneath the surface, the heat generated is also limited by the thickness of the layer. The commercially important ratio of radium to uranium in minerals is given as 700 milligrams of the former per ton of the latter, which is more than twice as great as the actual ratio. The present commercial price of radium is given as slightly more than 1000l. per grain, which is particularly unfortunate in such a book, since small quantities can be bought at the present time at about one-quarter or one-fifth this rate.
By J. P. Lord. Third edition. Pp. x + 103. (London: Harding, Bros, and Co., 1910.) Price 2s. 6d. net.