Scientific American, May 27, 1899, page 341:
General Greely, Chief of the Signal Corps, has made public the result of recent experiments with wireless telegraphy which have been tried by the Signal Corps of the United States Army. He states that since the announcement of the tests in space telegraphy by Signor Marconi, some two years ago, the subject has been under consideration, and recently experiments have been begun with the object of thoroughly testing the value of this means of communication for military and other governmental purposes. Special forms of apparatus have been designed and constructed for these tests and they have already shown sufficient promise to warrant further and systematic trials.
In the experiments thus far carried on, several forms of transmitters for the generation of the Hertzian waves have been used, and much promise has been realized from the use of a large alternating current coil as a generator instead of the ordinary Ruhmkorff coil employed by Marconi. This coil is energized by a three-quarters horse power rotary transformer furnishing an alternating current at 125 volts, and this arrangement makes a very powerful and efficient source of Hertzian radiation. The former receiver used has been substantially the Branley "coherer," discovered in 1891, and the signals transmitted are recorded upon a receiving tape. The transmitter has been mounted upon the western elevation of the State, War and Navy building, utilizing the present wooden flagpole as the vertical wire for the transmitter. The receiver was first placed at the old Naval Observatory grounds, about three-quarters of a mile distant, and later moved to the Signal Corps station at Fort Myer, Va. During the experiments constant communication was kept up by heliograph and flags between the transmitting and receiving stations, and this greatly facilitated the work of experimenting. Signals, letters, and words have been transmitted and received between these stations, but the great delicacy required in the present receiver has made the transmission of regular messages as yet unreliable and uncertain. The presence of large buildings and masses of iron and metal, necessarily present in cities, make such places undesirable for carrying out experiments of this character.
The distance over which signals may be transmitted by a given apparatus is governed by the height of the vertical wire used at either end, and this has naturally suggested the use of small balloons such as have already been used for signal and other purposes by the Signal Corps. A supply of these balloons has already been obtained, and will be used for this purpose in the near future. General Greely considers that the value of wireless telegraphy for communication between light houses and lightships and the shore is very great, especially where cables cannot be permanently maintained. For the signaling between ships at sea, and to replace ordinary flag methods in use between naval vessels, it should prove invaluable, since no kind of weather, fog, darkness, nor storm will affect its use, but that it will supplant to a material extent the use of wire for ordinary commercial telegraphy is not believed. The use of metal reflectors to augment and direct the radiation to particular points has already met with partial success, and should be thoroughly investigated. At present the radiation proceeds from the transmitter in all directions, and the same message can be received at any point within a proper radius at which a receiver is placed. A satisfactory reflector and a receiver of the proper electric capacity, or in other words tuned to the vibration of the particular transmitter, will make a great advance in space telegraphy. While secrecy of transmission is among the probabilities, the present stage of experiment does not justify its positive prediction.
Members of the Lighthouse Board stationed at Tompkinsville, Staten Island. N. Y., will in a few days begin a series of experiments intended to test the value of wireless telegraphy for use in lighthouses and lightships. One set of instruments will be set up in a station near St. George, and efforts will be made to communicate with the Scotland lightship. Other experiments will include the Sandy Hook and Fire Island lightships. If the experiments are encouraging, they will endeavor to communicate with the Highland lights. The instruments will be isolated as far as possible from other electrical apparatus and it is not believed that there will be anything in the intervening space between the instruments which will interfere with the signaling. The instruments used will be of the Clarke type, which we have already illustrated.