His instruments, which were wireless telephones--aerophones he called them--were to be made in pairs, twins that should talk only to each other.

They required no high poles, or balloons, or any other cumbrous and expensive appliance; indeed, their size was no larger than that of a rather thick despatch box.

And he had triumphed; the thing was done--in all but one or two details.
For two long years he had struggled with these, and still they eluded him.

Once he had succeeded--that was the dreadful thing.

Once for a while the instruments had worked, and with a space of several miles between them.