ee 
TRANSACTIONS OF SECTION G. 607 
been made from time to time to the British Association. Each specimen is in 
the form of wire 0:126 inch diameter and 70 feet long; and the figures obtained 
after two years’ exposure are :— 
Percentage increase of 
electrical resistance taken on 
value in 1911 at 15° C. 
Hich conductivity copper . 9 .  . . .  . 2:0 
Commercial aluminium . : Napanee : : . 44 
Duralumin ahaa ; ; 4 ; : ; 3 (Ore 
Duralumin is a copper-manganese-magnesium alloy of high tensile strength, 
and exposure has apparently made it more brittle. 
3. The Nature of the Electromagnetic Waves employed in Radiolele- 
graphy and the Mode of their Propagation. By Professor 
G. W. O. Howe, M.Sc. 
A very clear conception of the nature of the electro-magnetic waves employed 
in radiotelegraphy can be obtained by considering those electro-magnetic waves 
which exist in the space between the two conductors of a single-phase trans- 
mission line. If the conductors are flat, parallel strips, close together, and 
connected at the sending end to the terminals of an alternator, there is a certain 
yalue of the non-inductive load at the receiving end which will absorb the arriving 
energy without any reflection. Under these conditions the current and voltage 
are in phase all along the line, and the same is true if the line is assumed to be 
of infinite length. Line resistance and leakage are assumed to be negligible. It 
follows from this that the electric and magnetic fields at any point have their 
maximum values at the same moment. Instead of two parallel strips transmitting 
energy in one direction, two parallel discs of infinite extent can be imagined 
with the alternating P.D. applied between their centres. Energy would then be 
transmitted radially in all directions in the plane between the discs. The earth 
could take the place of the lower disc, while the upper one could be represented 
by a conducting horizontal plane some distance above the earth. The waves 
produced would be truly cylindrical, whereas those employed in radio-telegraphy 
are spherical. If, now, the upper disc is replaced by an inverted conducting 
cone of infinite extent, with its apex almost in contact with the earth, the alter- 
nating P.D. being applied between the apex and the earth, the electro-magnetic 
waves will be almost identical with those employed in radiotelegraphy and will 
vary in the same way with the distance from the sending station. This imaginary 
multi-directional transmission line, consisting of a lower plane (the earth) and an 
inverted cone, lends itself to simple calculation, because, like an ordinary trans- 
mission line, and unlike the two parallel discs, it has a constant inductance and 
capacity per mile. It can be shown that if the angle between the cone and the 
earth is 35 degrees, the relations between the magnetic and electric fields near the 
earth’s surface and the total energy radiated are identical with those existing in 
the ordinary radio-telegraphic wave. As in the transmission line already con- 
‘sidered, the current and P.D, will be in phase at every point, and therefore, 
contrary to the usually accepted view, the horizontal magnetic field and_ the 
vertical electric field due to a sending antenna are not 90 degrees out of phase 
but are approximately in phase, except in the immediate neighbourhood of the 
antenna. This also follows from the fundamental equations of a progressive, as 
distinct from a stationary, electro-magnetic wave. 
4. Atmospheric Refraction and Absorption as affecting Transmission in 
Wireless Telegraphy. By Dr. W. H. Ecci&s. 
5. Effect of Atmospheric Conditions on ihe Strength of Signals received 
at Liverpool from Paris and some other places, together with an 
Account of the Diurnal Variation in the Energy received, By 
Professor E. W. Marcuant, D.Sc. 
Measurements have been made over a considerable period of time, but those 
described herein deal mainly with observations during the month of July. The 
