J.Boulanger and G.Ferrie 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.
Sec.

2 The first, and not the least difficulty, is to clearly define the subject.

The words "wireless telegraphy," which at first seem to correspond to a simple and perfectly clear idea, may in reality apply to two series of questions, very different in the mind of a physicist, between which it is important to distinguish.