96. One of the very first questions asked in reference to a discovery is as to its practical utility. Already, we have important applications in one of the most humane directions, and that is in connection with diagnosis. Sciagraphs can also be employed in schools for the purpose of education, in some departments of anatomy, etc. The interest that it excites and the amusement that it affords are not to be overlooked, for anything in the nature of recreation possesses utility. However, we may greatly thank all experimenters who have investigated the subject, and who have not left its development alone to Roentgen; for predictions as to the utility of a discovery, however, apparently exaggerated, are very often proved, by subsequent developments, to have been underrated. Upon this point Prof. Boltzmann, in _Zeit. Elect._, Jan. 15, ’96, see also, _The Elec._, Lon., Jan. 31, ’96, p. 447, stated, “If we remember to what discoveries the most insignificant new natural phenomenon, such as the attraction of small objects by rubbed amber, of iron by the lode-stone, the convulsive twitches of a frog’s leg due to electric discharges, the influence of the electric current upon the magnetic needle, electro-magnetic induction etc., has led us, one can imagine to what applications an agent will be turned, which a few weeks after its discovery has given rise to such surprising results.” 97. Soon after hearing, (about the first of Feb. ’96,) of the Roentgen discovery, it occurred to the author to carry on experiments with fluorescence, but finding that it was inconvenient to work in a perfectly dark room, and, recognizing that black cardboard had practically no effect upon absorbing the X-rays, he devised a sciascope (_daily papers_, Feb. 13, and _Elect. Eng._, Feb. 19) which he afterwards learned was independently invented and used at about the same time by Prof. William F. Magie, of Princeton University, (see _Amer. Jour. Med. Sci._, Feb. 7, ’96 and Feb. 15, ’96) and by Prof. E. Salvioni, of Italy under the name of cryptoscope, (see _Med. Sur. Acad._ of Perugia, Italy, Feb. 8, ’96.) In about a month afterwards (_Elect. Eng._, N.Y., Apr. 1, ’96, p. 340) the instrument (with phosphorescent calcic tungstate § 13. in place of fluorescent barium platino cyanide) was again published under the name of the Edison fluoroscope. There are probably many other claimants—some professor in London—name forgotten. They all consist of a tapering tube with a sight hole at one end and a fluorescent screen in the other, which is closed by opaque card board. (Frontispiece at Chap. X). For the sake of conformity, the words sciagraph and sciagraphy and similar derivatives, and in view of the meaning of the radical definitions, have been employed throughout the book. The objection to the word fluoroscope is that the instrument is practically universally employed in seeing the shadows of objects, otherwise invisible to the naked eye, rather than to test fluorescence.