With his wizard camera Tom did much to advance the cause
of science. His great searchlight was of great help to the
United States government in putting a stop to the Canadian
smugglers, while his giant cannon was a distinct advance in
ordnance, not excepting the great German guns used in the
European war.

When Tom perfected his photo telephone the last objection
to rendering telephonic conversation admissible evidence in
a law court was done away with, for by this invention a
person was able to see, as well as to hear, over the
telephone wire. One practically stood face to face with the
person, miles away, to whom one was talking.

The volume immediately preceding this present one is
called: "Tom Swift and His Aerial Warship." The young
inventor perfected a marvelous aircraft that was the naval
terror of the seas, and many governments, recognizing what
an important part aircraft were going to play in all future
conflicts, were anxious to secure Tom's machine. But he was
true to his own country, though his rivals were nearly
successful in their plots against him.

The Mars, which was the name of Tom's latest craft, proved
to be a great success, and the United States government
purchased it. It was not long after the completion of this
transaction that the events narrated in the first chapter of
this book took place.

Mr. Damon and Tom had been firm friends ever since the