WIRELESS TELEGRAPHY. 
123 
Marconi's coherer (Plate II.) consists of a small glass tube li inches 
long and about T \> inch internal diameter. In it are tightly fitted two 
silver plugs whose faces are separated by about inch. The small 
space between them is half filled with fine metallic filings, chiefly of hard 
nickel, with a small admixture of silver. The air is exhausted from 
the tube until a considerable vacuum is produced, and the tube is then 
sealed. A vacuum is not absolutely necessary, but desirable. In my 
opinion its object is to ensure that the interior of the tube is quite dry. 
The action of the coherer when oscillations are excited through the tube 
has been previously described. The terminals of the tube are con¬ 
nected in simple circuit with a single dry cell and a “ relay " of Post 
Office pattern. The current through this simple primary circuit is not 
sufficient to actuate the relay, until the oscillations are excited. When 
this occurs, the relay tongue moves over, and establishes a current 
through a local circuit containing a “ tapper," and a comparatively 
powerful battery. The function of the “ tapper " (constructed like an 
electric trembling bell) is to strike the coherer and bring about me¬ 
chanical de-coherence i.e., restitution of the coherer to normal non¬ 
conducting state. Therefore as long as waves fall on the coherer the 
tapper continues to strike it, and the motion of the tapper ceases when 
the electrical waves cease. 
The sound made by the tapper is generally sufficient to en¬ 
able the signals to be read, but should it be necessary to record the 
signals, a “ Morse inker " is placed in parallel with the tapper and the 
signals are then registered on a tape according to the Morse code. 
In the diagram—Plate II—the Morse inker is not shewn. 
(Experiment:—The action of the tapper on a receiving apparatus 
placed in the theatre was shewn.) 
To ensure successful signalling over any but quite short distances 
there are a number of details to be attended to which it would be out 
of place to enter into here, and I think it is time now to give you some 
idea as to what has been done up to the present. 
Mr. Marconi has kindly furnished me with the following statement:— 
At Salisbury good readable signals were transmitted a distance of from 
5 to 6 miles during a series of experiments early in the year. More 
recently he tells me a distance of 8 miles has been covered at the same 
place. Some experiments were made in signalling across the Bristol 
Channel near Cardiff. Success was achieved in transmitting signals 
from Lavernock to Flatholm, 3£ miles, and subsequently from Laver- 
nock to Brean Down, 9 miles. I am, by the kindness of Major Carr, 
able to show the records of two of the actual signals sent from Laver¬ 
nock to Flatholm on 13th May, 1897. (Tape records shewn.) It will 
be seen that the messages are perfectly readable by anyone acquainted 
with the Morse code. 
At Spezzia, in Italy, messages have been sent from ship to shore, a 
distance of 12 miles, and I am told that the Italian Government are 
giving the system a practical trial for naval purposes. 
The most recent experiments carried out by the General Post Office 
have taken place at Dover, but the main object of these appears to 
