192 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
time past employed such directive antenne at his large power stations 
at Poldhu and elsewhere. : 
These, then, are a few of the contributions which have recently 
been made by practicians and theorists to this fascinating and pro- 
gressive subject. But whilst we may congratulate ourselves that 
progress continues to be made, there are still large districts of it in 
which our knowledge is most incomplete. One matter having a very 
practical bearing is the necessity for systematic study of the causes 
which vary the transparency of space to long electric waves. You 
will continually see references in the daily papers to isolated feats of 
communication between ship and ship, or ship and shore, over un- 
usually large distances. Ships equipped with what is called short- 
distance apparatus, that is intended to send and receive over 200 
miles or so, are able occasionally to communicate with others 600, 800, 
or even 1,000 miles away. This is 
60° not altogether a matter of personal 
skill or of apparatus. Our terres- 
trial atmosphere varies from day to 
day and hour to hour in its trans- 
parency to long telegraphic electric 
waves, just as it does to the short 
light waves. One reason, and prob- 
ably a valid one, which has been ad- 
vanced for this is the ionization of 
the atmosphere by sunlight, radio- 
300° 
i active matter, or matter electrically 
<< charged reaching our earth from 
ws the sun or cosmical space. ‘These 
Fic. 22.—Polar diagram for Braun’s ions or electrically charged par- 
Dace hts ticles suspended in the air are set 
in motion by the electric force of long electric waves passing 
through the region. This, however, involves energy which must 
be taken from the wave, and hence the wave passes on so much the 
weaker. This effect is altogether different from the disturbing effects 
of atmospheric electricity on the receiving antenna. As first noticed 
by Mr. Marconi on one of his Atlantic voyages, the atmospheric 
transparency for long electric waves is decreased by daylight and 
this reducing effect of light on the wave energy takes place chiefly 
near the transmitting antenna where the electric force is largest. It 
fluctuates from hour to hour and month to month according to laws as 
yet. undetermined, and has no doubt secular and irregular fluctuations 
superposed on its regular variations. The subject of long-distance 
wireless telegraphy is yet too young to provide observations for any 
