so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennæ suitably differing in their phase of excitation and situated at the vertices of a

FIG. 98.-Arrangement of Bellini and Tosi for directive wireless telegraphy.

triangle it is possible to send strong signals in certain directions only.

Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are

incoming and to the condenser, spark gap and coil when the signals are to be transmitted.

Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves come. These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in

the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.

By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.

The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and

transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.

CHAPTER VI.

THE DIGNITY OF WIRELESS. ITS APPLICATIONS AND SERVICE. WIRELESS IN THE ARMY AND NAVY.

WIRELESS ON

AN AEROPLANE. HOW A MESSAGE IS SENT

AND RECEIVED.

Wireless telegraphy and that precocious infant, wireless telephony, have outlived all the speculative and tentative achievements of their early days and have established themselves in an important and settled position among our methods of conveying intelligence.

The field has been so greatly enlarged in recent years and the apparatus and methods so improved that the broadest possible view of its future development and importance

FIG. 100. Special light weight wireless telegraph set for airship

service.

is justified. And there must inevitably come the time when our merchant marine and wireless service will come under such reasonable regulation that it will be removed from any dependence upon stock jobbing wireless telegraph and telephone companies.

Official sources show that the equipping of sea-going

vessels with wireless apparatus is progressing at a rapid rate and it is not difficult in the face of certain facts to appreciate the enormous volume of business that sooner or later will be handled by wireless. Three hundred and sixty-three United States naval vessels and about eight hundred merchant vessels are equipped at this writing. The large number of commercial shore stations, army forts and posts, and those used by corporations, isolated stations, etc., for various private purposes comprise a list which reaches an enormous total.

Whatever may have been the status of wireless previous