404 TRANSACTIONS OF SECTION A. 
telegraphic signals, and substituting for the simple telephonic receiver and 
rectifier or magnetic detector a visual signal or supplementing it by a loud- 
sounding call. 
(il) On Wireless Telegraphy. By Professor Dr. A: SomMMERFELD. 
Der Verfasser versucht von seinem theoretischen Standpunkte aus, die 
verschiedenen von Professor Fleming formulirten Fragen zu beantworten. 
Er halt an der Hoffnung fest, dass die Maxwell’schen Gleichungen unter 
einfachsten Annahmen iiber das Verhalten der Erde und Luft im Stande sind, 
von den praktischen Ergebnissen der drahtlosen Telegraphie Rechenschaft zu 
geben. Diffraction, Oberflachenwellen und Hertz’sche Raumwellen lassen sich 
in der strengen Lésung der Maxwell’schen Gleichungen nicht von einander 
trennen, sind veilmehr durch die Bedingungen an der Grenze zwischen Luft und 
Edre miteinander notwendig verknipft. 
Eine von dem Verfasser veranlasste Untersuchung von H. W. March ist 
dahin zu berichtigen, dass zu der von March urspriinglich angegebenen Formel 
ein exponentieller Zerstreuungsfaktor hinzutritt, der dieselbe Form hat, wie in 
den Untersuchungen von Poincaré und Nicholson. Bei grossen Wellenlingen 
ist dieser Faktor nicht so gross, dass er, wie man angenommen hat, die prak- 
tische Ueberwindung der Erdkrimmung unméglich macht. Vielmehr scheint 
er mit den Messungen von Austin der Gréssenordnung nach tibereinzustimmen. 
Die Mitwirkung von Oberflichenwellen kommt in dem March’schen Resultat 
ebenfalls zum Ausdruck. 
Der Unterschied der Ausbreitung tiber Land und Wasser dirfte durch die 
Rechnungen des Verfassers (Ann. 28) erklart sein. Die Ionisation der oberen 
Luftschichten kann die Ueberwindung der Erdkriimmung nicht erklaren. Die 
Theorie des gerichteten Senders von Horschelmann scheint dem Verfasser 
zuverlassig. 
(ii) On certain Phenomena accompanying the Propagation of Electric 
Waves over the Surface of the Globe. By W. H. 
Eccurs, D.Sc. 
The purpose of this paper was to describe some of the phenomena met with 
in the transmission of electric waves, natural and artificial, over great dis- 
tances, and to examine how far they may be accounted for by the ionisation of 
the air through which the waves travel. The importance in this connection of 
the natural ionisation of the air has only recently had attention drawn to it in a 
paper read by the author before the Royal Society in June. In this paper it was 
shown that the velocity of electric waves through ionised air exceeds their 
velocity through un-ionised air by a percentage proportional to the concentration 
of the ions. Assuming that the ionisation due to solar radiation increases with 
increase of height above the earth’s surface, it follows that a vertical wave- 
front will tend to tilt forward as it travels. It is found that the consequent 
curvature of the trajectory of waves travelling nearly horizontally will work 
out at about the curvature of the earth for quite reasonable values for the 
concentration of the ions. The trajectory is more curved the lower the fre- 
quency of the waves, being, in fact, inversely proportional to the square of 
the frequency at high levels, but probably varying much less rapidly with fre- 
quency at the low levels. In order to account for the great difference between day 
and night transmission it seems necessary to suppose that there exists in the 
upper atmosphere a permanently ionised layer that is not dependent on solar 
radiation for its maintenance—a suggestion due to Heaviside. Some justifica- 
tion for this assumption was adduced in the present paper from facts quite distinct 
from wireless telegraphy. Taking this hypothesis with the hypothesis of 
refraction by ionised air, many phenomena can be explained without appeal to 
the principles of diffraction or to absorption in the air or by the earth’s surface. 
Some of the most remarkable and impressive phenomena yet brought to 
light by wireless telegraphy are the fluctuations of signals and of strays at twi- 
light, in the night, or during an eclipse of the sun. These especially were 
discussed in the paper. Many of the observed facts can be explained tolerably 
well by aid of the hypotheses described. 
