An example of yesterday seems to show the difficulties of such a task. Among recent discoveries the invention of wireless telegraphy is one of those which have rapidly become popular, and looks, as it were, an exact subject clearly marked out. Many attempts have already been made to write its history. Mr J.J. Fahie published in England as early as 1899 an interesting work entitled the _History of Wireless Telegraphy_; and about the same time M. Broca published in France a very exhaustive work named _La Telegraphie sans fil_. Among the reports presented to the Congrès international de physique (Paris, 1900), Signor Righi, an illustrious Italian scholar, whose personal efforts have largely contributed to the invention of the present system of telegraphy, devoted a chapter, short, but sufficiently complete, of his masterly report on Hertzian waves, to the history of wireless telegraphy. The same author, in association with Herr Bernhard Dessau, has likewise written a more important work, _Die Telegraphie ohne Draht_; and _La Telegraphie sans fil et les ondes Électriques_ of MM. J. Boulanger and G. Ferrié may also be consulted with advantage, as may _La Telegraphie sans fil_ of Signor Dominico Mazotto. Quite recently Mr A. Story has given us in a little volume called _The Story of Wireless Telegraphy_, a condensed but very precise recapitulation of all the attempts which have been made to establish telegraphic communication without the intermediary of a conducting wire. Mr Story has examined many documents, has sometimes brought curious facts to light, and has studied even the most recently adopted apparatus. It may be interesting, by utilising the information supplied by these authors and supplementing them when necessary by others, to trace the sources of this modern discovery, to follow its developments, and thus to prove once more how much a matter, most simple in appearance, demands extensive and complex researches on the part of an author desirous of writing a definitive work. § 2