Secondly, the author often imagined that he was writing in behalf of the surgeon and physician and those who intend to experiment, especially when he found in his investigations of recent publications descriptions in detail of the electrical apparatus employed in experimenting with X-rays. He improved the opportunity of repeating the statements of the difficulties, and how they were overcome; also, the precautions necessary to be taken, and, besides, the kind of discharge tubes and apparatus best adapted for particular kinds of experiments. The chapter on applications in diagnosis and anatomy, etc., is of especial interest to physicians.
Thirdly, as the discovery of the Roentgen rays has established a new department of photography, those who are interested in this art may be benefited by the results and suggestions disclosed in connection with photographic plates, time of exposure, adjuncts for best results, precautions for obtaining sharp shadows, and steps of the process, from beginning to end, for carrying on the operation.
Fourthly, expert physicists and electricians, professors, etc., need something that the above classes do not, and this is the reason why the author has not assumed the burden of carrying any line of thought or theory from the beginning to the end of the treatise, nor has he made the book in any way a personal matter by criticising experiments, nor even by favoring the views of one over the other, unless it is in an exceptional case here and there; but in each instance the investigator’s name is given, and that of the publication in which the account may be found, so that the scientist may refer thereto to test the correctness of the author’s version of the matter, or to learn the nature of the minute details and circumstances.
The author suggests that the study of the phenomena of the discharge tube would not be amiss in scientific schools and colleges. He argues that in view of all experimenters in this line having been made enthusiastic and fascinated by reason of (1) the beautiful effects, (2) the field being always open to new discoveries, (3) the direct practical and theoretical bearing of the peculiar actions upon other departments of electricity, light, heat, and magnetism, (4) the pleasure in attempting to obtain results reported by others, and especially the large amount of valuable theoretical and practical instruction resulting therefrom, by repeating the experiments or studying them, and (5) the possible applications of the discharge tube in connection with electric lighting and in the new department of sciagraphy by X-rays, and for other good and valuable considerations—it follows that students who have been through or who are studying a text-book of physics and electricity would be greatly benefited by a course in the discharge-tube phenomena.
In view of the large amount of dictation necessary in order to complete the work in such a short period, and in order that the subject-matter might involve the treatment of the latest work of the French and German as well as of the English and American, and inasmuch as the journals of the latter did not always contain complete translations and, for better service in behalf of the readers, the authorship was shared with others, and, therefore, much credit is due to Prof. Anthony for final chapter, to Mr. Louis M. Pignolet for assistance in connection with French periodicals and academy papers ([§ § 63a], [84], [99], [101a], [103a], [112a], [124a], [128], at end, [139a], [154], [155], [156], [157], [158], and [159]); to Mr. N. D. C. Hodges, formerly editor and proprietor of Science, who obtained some pertinent accounts, ([§ 97a], [97b], [99A], [B], [C], [D], to [99T], inclusive) by investigations of recent literature at the Astor Library, New York; and also to Mr. Ludwig Gutmann (Member American Institute of Electrical Engineers) for a few translations from the German.
Credit is given in each instance to all societies and publications by naming them in the respective paragraphs herein. In nearly every case the author prepared his material from original articles and papers contributed by the investigators to the societies or periodicals.
The author has prepared himself to withstand, with about half as much patience as he expects will be required, all criticisms based upon disappointments which may be experienced by the true, or the alleged true, first discoverer of any particular property of the electric discharge not duly credited. He has been particular in presenting knowledge as to physical facts and principles, but not equally, perhaps, as to the originator of the experiment, or as to the actual first discoverer, for the simple reason that the book is in no sense a history not a biography. Where the paragraph has been headed, for example, “Swinton’s Experiment,” it means that that party (according to the article purporting to be written by him) made that experiment. Some one else may have made exactly the same experiment previously, yet the instruction is equally as valuable as though the researches of the first discoverer had been related. On the other hand, the author has never had any intention of giving credit to the wrong party. The dates in the captions indicate the general chronological order in behalf of those thus interested. With this explanation, it is thought that the claimants will be much more lenient in their criticisms concerning priority of discovery. While the developments have generally followed each other historically, as well as appropriately for the purpose of instruction, yet now and then it was preferable to place the description of a comparatively recent experiment in conjunction with some description of an experiment made at a much earlier date. For this reason, also, the book is not of a chronological nature. The subject-matter, as usual, is divided into chapters, but the sections are to be considered as subordinate chapters, having different shades of meaning, and the one not necessarily bearing a direct relation to the contents of its neighbor, but as, in a novel or a treatise on geometry, having its important part to play in conjunction with some later or preceding section.
Edward P. Thompson.
Temple Court Building, New York,
August, 1896.