In the accompanying illustration is shown a portable outfit for wireless telegraphy, designed by Mr. Marconi and especially adapted for military requirements. It is an outgrowth of experience in the South African war and is described by an English correspondent of the Scientific American, to which journal the Western Electrician is indebted for the particulars here given. For some time past Marconi has been experimenting with cylinders to act as receivers in lieu of the high wire or antenna. These cylinders have been proved to be more efficacious for the transmission of messages over short distances, than the ordinary apparatus. When the electric currents are excited, the waves at first oscillate very rapidly and violently, but in a few moments the vibrations die down, or become damped, in much the same way as the wire of a piano decreases its vibrations after a note has been struck. It is imperative that these vibrations should be sustained as much as possible, in order to travel over a long distance, and to insure this end there must be a great capacity in the sending instruments. The effect of the cylinder is to render greater capacity than the ordinary aerial wire, and consequently to secure more sustained vibrations.
The automobile shown in the illustration is the Thorncroft steam-motor car, or lorry, which is now so much used in England for heavy road traffic. The car has a capacity for about five tons, and can attain a speed of from 12 to 14 miles an hour with a full load. The rear part of the lorry is fitted up as an operating room, containing instruments and electric batteries. Upon the roof of the car the long cylinder is placed. In the picture the cylinder is shown raised ready for use, but when not required it is laid down flat upon the roof, out of the way. The cylinder is about 25 feet in height. It is constructed of metal and thoroughly insulated. The points from which the currents are transmitted into, and received from, space may be observed at the top of the cylinder, and wires connect them with the instruments below. One special recommendation of this migratory installation is that communication can be maintained while the vehicle is traveling. The maximum distance over which messages can be dispatched and received by means of this installation is 20 miles at present, which is generally sufficient for military purposes. Marconi, however, is still continuing his experiments with a view to increasing this distance. The cylinder is said to perform exactly the same functions as the aerial wire, even in connection with the tuned or synchronized messages.
Although Marconi is still continuing his investigations with the cylinders, his principal experiments are still concerned with the perfection of the original system. Although Marconi has found the cylinders to be specially valuable for the transmission of messages over short distances, up to about 30 miles, it has not been found so successful in the case of long distances.