302 Timehri. 
state these filings did not make contact between the plugs and consequently 
the circuit was not complete ; but as soon as an electrical discharge occurred 
in the neighbourhood of the coherer the filings cohered and made contact with 
the plugs, thus completing the circuit and allowing the current to flow and so 
cause the galvanometer needle to be deflected. 
We now come to the advent of Marconi and the birth of practical Wireless 
Telegraphy. Many people have an idea that wireless was a thing unthought of, 
until suddenly discovered and perfected by Marconi, whereas, as you have 
already seen, it was the work not of one man, but of a long line ot scientists, 
each, so to speak, forging his link in the chain, then stepping aside to make 
room for his successor. Maxwell developed the theory of ether waves ; Hertz 
experimentally confirmed the theory. Righi improved upon Hertz’s oscillator 
and Branly produced a practical instrument for detecting the waves. Sir 
Oliver Lodge, in 1894, actually sent and received messages by ‘‘ Wireless,” 
but does not seem to have fully realized the importance of his achievement 
at the time, and it was not until some few years later that the scientist in 
collaboration with an eminently practical man, in the person of Dr. Alexander 
Muirhead, made his system a success. Sir Oliver Lodge’s coherer is on a differ- 
ent principle from that of Branly. It consists of a steel wheel revolving over a 
tube containing mercury. The wheel rests very lightly on the mercury but 
does not make metallic contact with it, owing to a very fine film of oil separat- 
ing them. The coherer is connected in a circuit somewhat similar to that 
already described, the wires being connected, one to the steel wheel, the other to 
the mercury, instead of to the two metal plugs. The oscillations break down 
the insulation of the film of oil, and the wheel and mercury making metallic 
contact complete the circuit, so allowing a local battery and telegraph instru- 
ment to come into play. The circuit is broken when the oscillations cease 
by the revolving wheel causing the oil to regain its position. 
Captain Jackson, R.N., working independently, succeeded, in 1895, in send- 
ing and receiving messages between ships at sea but his results were made 
known only to the naval authorities. 
In 1896 Marconi took out his first English patent, and carried out a long 
series of tests with the co-operation of Sir William Preece, at that time the 
Engineer-in-chief of the Post Office, and ‘“‘ Wireless’”’ began to be looked at 
from a commercial point of view. 
Marconi’s coherer was on the same principle as Branly’s, but, in the hands 
of the younger scientist, it became a far more reliable and sensitive instrument. 
Marconi replaced the metal plugs used by Branly with ones of German silver, 
and the iron filings with a mixture of nickel and silver. By withdrawing the 
air from the tube, he made the coherer more sensitive and rendered it capable 
of adjustment, by making the gap containing the filings V-shaped. 
This coherer was joined in circuit with a battery and relay, and in the local 
relay circuit was placed a telegraph instryment. The terminals of the co- 
herer were also connected to two metal plates or capacity areas. The radia- 
tions from the transmitting station affected the coherer, and the filings m kinv 
