While thus retreating step by step he runs the risk of losing himself in the night of time.
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 Congres 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 Electriques_ of MM.