loss of one fifth in efficiency they are on an equality with locomatives at sixty miles an hour; below that speed the locomotive is to be preferred; beyond it, the motor is the cheaper servant.
While this work shows evidence on every page of the scientific mastery of its subject, the authors are plainly men desirous of meeting the practical difficulties which the operation of electric railways presents every day. They are also fully aware that the investor is less interested in the analysis of electrical machinery than in the simple question, Will it pay? Commercial considerations receive full and sensible treatment. Others than superintendents and investors can read this work with profit. It is as good an example as American literature contains of scientific principles applied to the solution of practical problems—problems, too, as important in their social as in their commercial bearings. Progress in electric traction means the relief of congested cities, the expansion of wholesome suburbs, on a scale impossible to the steam locomotive. In long-distance service it stands for an advance second only to that due to George Stephenson.
Scientific Correspondence of Joseph Priestley. Edited, with Copious Notes, by Henry Carrington Bolton. New York: privately printed. Pp. 240. Price, $2.50. E. F. Brown, 180 Warren Street, Brooklyn, Agent.
The "Father of Pneumatic Chemistry" expected to be remembered chiefly for the theological views which he put forth, having been in early life a Unitarian minister, and a writer on theological subjects throughout his career. Hence his modest autobiography, which was expanded into two volumes, with the addition of several hundred letters, by his son and J. T. Rutt, contains almost nothing about his scientific investigations. To supply the lack of material relating to his work in the latter field, Dr. Bolton has collected ninety-seven letters, nearly all written by Priestley, his correspondents being Josiah Wedgwood, Captain James Keir, Sir Joseph Banks, and others in England, and Dr. Benjamin Rush and others in America after he came to this country. They contain many interesting details concerning the progress of his researches on the gases, several of the most important of which were discovered by him. The letters are supplemented by many biographical, bibliographical, and explanatory notes by the editor, and the volume contains a portrait of Priestley and one of Josiah Wedgwood. There is also a synopsis of correspondence of Dr. Priestley, consisting chiefly of letters from him to his brother-in-law, Mr. Wilkinson, from 1790 to 1802. An appendix contains a descriptive list of the likenesses of Joseph Priestley in oil, ink, marble, and metal, embracing ninety-three items; an account of the Lunar Society, in Birmingham, founded by Matthew Boulton, Erasmus Darwin, and others, and of which Priestley was a member; and an inventory of Dr. Priestley's laboratory, which was sacked by rioters in 1791.
Diphtheria: its Natural History and Pretention. By R. Thorne Thorne, F. R. S. London and New York: Macmillan & Co. Pp. 266. Price, $2.
Statistics show that the death-rate from diphtheria in England and Wales has been increasing during the last twenty years, and more rapidly in the cities than in the country. This disease thus presents a contrast to the majority of zymotic diseases, the death rate from which has been lessened as physicians have gained more knowledge of their nature and as sanitary conditions have been improved. In view of its fatal and little understood character, the author has undertaken to collect what is known in regard to diphtheria. It appears that the broad geological features of a district have no influence on the development or diffusion of the disease. A chart prepared by Dr. G. B. Longstaff shows that the death-rate has been high in some counties and low in others on the same geological formation. Yet the author is convinced that a surface soil which retains wetness and organic refuse, together with an aspect exposed to cold wet winds, tend to the fatality of diphtheria. He further discusses the general nature of the disease, its relation to scarlet fever and to croup, the influence of schools in spreading the infection, and milk as a vehicle in which it may be carried. The measures of prevention which are suggested by his study of the subject are stated in detail, and his general conclusions as to the natural history of diphtheria are also given. The volume contains