TRANSACTIONS OF SECTION A. 403 
with the Morse signals, the receiving operator hears long or short musical 
sounds, which he can interpret into the letters of the alphabet. 
The wireless message is thus picked up at the receiving station by hearing 
telephonic sounds due to a greater or less number of trains of high-frequency 
oscillations in the transmitting antenna corresponding to dashes or dots in the 
Morse alphabet. 
These long or short groups of oscillations in the transmitting antenna create 
similar groups in the receiving antenna, which, when rectified, cause gushes of 
electricity in one direction through the telephone, and therefore make sounds 
like ticks or musical notes of long or short duration. The pitch of this note is 
the frequency of the spark at the sending station. 
As long as short distances only were being covered by the use of the above 
apparatus a sufficiently satisfactory explanation of it was found in the properties 
of Hertzian waves. When, however, Mr. Marconi in 1901 sent the first signals 
across the Atlantic, and later achieved the feat of signalling 6,000 miles from 
Ireland to South America, the question arose how such waves, if they are true 
Hertzian waves, are propagated a quarter of the way round the earth. The 
mathematical investigations of Professor Macdonald, Lord Rayleigh, the late 
Professor H. Poincaré, and of Dr, Nicholson seem to have proved that diffraction 
alone will not account for the phenomenon, even although the electric waves 
used, as by Marconi, have a wave-length of nearly four miles, or the two- 
thousandth part of the earth diameter. Another theory has been developed by 
Professor A. Sommerfeld, starting from an assumption that the usual earthed 
transmitter may be regarded as a Hertzian oscillator at the boundary of two 
dielectrics of different nature. His theory leads to the conclusion that there are 
not only space-waves (Raumwellen) in these media, but also surface-waves 
(Oberfldchenwellen) at the boundary surface, and that these latter vary in 
amplitude inversely as the square root of the distance, and are sufficiently feebly 
damped in a horizontal direction to be propagated long distances, irrespective of 
irregularities of surface. Hence they are not affected by earth curvature. 
Objections have been raised to Sommerfeld’s theory on the ground that these 
surface-waves have not been experimentally demonstrated, but it is evident that 
they resemble the surface-waves which can be produced on sheets of metal. A 
third theory of long-distance electric-wave propagation has been based upon 
the ionisation of the atmosphere. 
Dr. Eccles has shown that in a medium containing free ions of a certain kind 
the electric-wave velocity may be greater than that of the wave in the same 
dielectric un-ionised. Hence the upper part of a wave surface travelling over the 
earth may have a greater velocity than the lower part if it should happen that 
the upper atmosphere is ionised, as it most probably is, by ultra-violet light. The 
waye may, therefore, follow round the earth’s curvature to a greater or less 
extent. 
_ Closely connected with this is another imperfectly solved problem in con- 
nection with long-distance radiotelegraphy, viz., the reason for the inhibiting 
effect of daylight. An explanation has been sought in the discharging effect of 
light upon the antenna, and also in the absorption of wave energy produced by 
atmospheric ionisation. It can, however, be shown that no atmospheric con- 
ductivity yet measured at earth-level, or some moderate height, is sufficient to 
produce the absorption required by observation. An explanation may be sought 
in the refraction of the long electric-waves by the varying dielectric constant 
produced by ionisation of the atmosphere by ultra-violet light at various levels 
of the atmosphere, which would curve the ray more or less out of agreement 
with the earth’s curvature and hence reduce its range. 
_. There are many phenomena, such as the greatly reduced signalling distance 
at_ dawn and dusk and the inequality in signalling distance in a north-south and 
east-west direction observed by Mr. Marconi, which have not yet been explained 
on any theory. Other questions which may be thrown down for discussion are 
those of the theory of directive antenne, such as those of Marconi and Bellini 
and Tosi, and also the location of the direction of the arriving radiotelegraphic 
waves, 
The problem of radiotelephony seems in a fair way of solution by means 
of improved arc-generators and of high-frequency alternators. Also practical] 
improvements have lately been made in recording by various means the radio- 
DD 2 
