WIRELESS TELEGRAPHY. 
121 
matter of conjecture, but it would appear as if the oscillations induced 
through the metallic filings cause the films between these fine par¬ 
ticles of metal to break down and produces partial welding together 
or cohesion of the filiugs—hence the name “ coherer,” the most apt 
name that I think could be given to it. 
All the facts which I have just mentioned were in possession 
of the scientific world before Marconi showed that intelligible signals 
could be sent over distances exceeding one mile. Previous to this the 
distance signalled was about 40 yards, and the opinion appeared to be 
held by scientists of the highest repute that half a mile was about the 
limit. There would appear to be a tendency on the part of some 
scientists to deny credit to Mr. Marconi on account of these facts being 
previously known; but it is undoubted that Mr. Marconi was the first 
to produce apparatus on the above-mentioned lines by which readable 
signals could be produced over a useful distance, that is more than one 
mile. 
Here I would draw attention to a point frequently lost sight 
of, that it is a great step from simply detecting waves with this appar¬ 
atus to making this apparatus record organised signals conveying an 
intelligible message. The credit for this would appear to be due to Mr. 
Marconi, thus raising an instrument from the rank of a scientific curiosity 
to that of a practically useful piece of apparatus (loud applause). 
Let me give you a short description of the Marconi apparatus 
(see Plate II). 
(The second diagram was thrown on the screen.) 
The transmitter is a modification of the pattern devised by Professor 
Righi. The oscillations are produced across a system of four solid 
brass spheres. The gap between the two centre spheres is about a 
millimetre long; the outer gaps are longer and adjustable according 
to the spark length employed. Connection is made to the secondary 
of an induction coil capable of giving a spark up to about 10 inches in 
length. A simple key is inserted in the primary circuit, on pressing 
which for a short or long period, a stream of sparks of short or long 
duration may be produced across the spark gaps of the transmitter, 
thus causing radiation of the waves under definite control. The short 
and long discharges correspond to the dots and dashes of the Morse 
code. 
Two points about the transmitter will attract attention. First 
of all there is the parchment jacket filled with rosin or vaseline oil which 
surrounds one half of the centre spheres. The main object of the oil 
bath is to keep the surface of the centre sphere clean and polished. 
It is essential for the production of this electrical radiation that the 
spark shall “ snap ” across very sharply, and to secure this the sur¬ 
faces between which the spark passes must be kept clean, smooth 
and highly polished. Secondly the wings.” These are very much 
in evidence and attract the eye at first more than anything else. As 
a matter of fact the instruments within this theatre would work pro¬ 
bably as well without these wings. Their object may be stated to be : 
(1), to lengthen the line along which the oscillations take place, and in 
