37o SCIENCE PROGRESS 



communicate except with the aid of especially powerful 

 apparatus. It will be seen, therefore, that we have by no 

 means as yet even determined all the abnormalities of the 

 effects, far less reached a final explanation of them. 



There are many geophysical facts which seem to indicate 

 that the upper layers of the earth's atmosphere are in a highly 

 conductive condition. We have in the first place the phenomena 

 of the Aurora, which is generally allowed to be an electrical 

 discharge and although its principal manifestation is in higher 

 latitudes, yet, as W. W. Campbell showed in 1895, the green 

 auroral line \ 5,770 can be seen on moonless nights in any 

 part of the sky. Then, again, we have Prof. Schuster's 

 conclusions from observations of terrestrial magnetism that the 

 greater part of the diurnal variation must be due to electric 

 currents in the upper atmosphere ; also the suggestions of 

 Arrhenius and of W. J. Humphreys that the outermost layers 

 of our atmosphere are kept permanently ionised either by 

 electrons shot out from the sun or by the bombardment of 

 cosmical dust. Prof. Schuster's conclusion is that at a height 

 of about 100 km. the atmosphere conductivity is of the order 

 of io~ 13 electromagnetic units, equivalent to 10,000 ohms per 

 centimetre cube; Dr. Eccles, working from this basis, finds that 

 this conductivity would suffice to give sufficient refractive power 

 equivalent to reflection for radiotelegraphic waves. 



Hence it appears as if a complete explanation of long-distance 

 radiotelegraphy and of the variations introduced by daylight 

 is intimately bound up with a knowledge of the state as regards 

 conductivity, dielectric constant and ionisation of the air at 

 very high levels. Our methods of direct exploration by balloons 

 are probably limited to altitudes of 7 or 8 miles, hence all our 

 knowledge of effects and states at a height of 40 or 50 miles 

 will have to be derived by inferences drawn from observations 

 of terrestrial magnetism, electricity and geophysics generally. 



Furthermore, recent experiments by Dr. H. Lowy and others 

 have shown that electromagnetic waves may be used to explore 

 the crust of the earth and perhaps locate masses or veins of 

 metallic nature. A better knowledge of the function of the earth 

 in wireless telegraphy is therefore necessary as a basis for theory. 



Sufficient will have been said in this article to show that 

 whilst radiotelegraphy has proved to be a weapon of enormous 

 value for supermarine intercommunication, for saving life at 



