It is now generally admitted that the range of radio-transmission of signals is materially influenced by solar radiation; not only in regard to false signals or "X's"; but also in regard to the attenuation of the transmitted electro-magnetic waves. This attenuating influence of solar radiation on the transmitted waves ordinarily consists of (1) a nearly steady action during the daytime, together with (2) certain marked disturbances occurriny near sunrise, or sunset, or both. In regarn io the

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... st or steady effect, we may consider that during the day, whatever the weather may be; i. e., the conditions of wind, temperature, pressure, cloudiness or precipitation in the first few kilometers of air nearest to the ground surface, the sun's rays are steadily falling upon the upper layers of the air; where the air density is relatively very low. It is known from physical laboratory experiments, that ultra-violet light, passing thru attenuated air, ionises it; or decomposes electrically neutral air molecules into positive and negative constituents, the energy of decomposition being absorbed from the radiation. If the ultra-violet radiation is then withdrawn, these constitutents attract each other and recombine, perhaps converting the energy of recombinaion into heat energy or molecular oscillations. For a given intensity of received radiation of assigned wave-length in the ultra-violet region of the spectrum, we may suppose that there exists, in the final state, a certain corresponding number of free electrons per unit of air-volume. It is also reasonable to consider that after the ultra-violet rays in the sunlight have penetrated deeply into the air, they become: (1) scattered and diffusely reflected by the air-m-olecules, thereby giving us the blue color of the clear sky, and (2) absorbed in decomposition and ionisation of the air-molecules. Consequently, but little ultraviolet light from the sun reaches the ground, after passing thru the atmosphere. The solar spectrum at the ground, or ocean level, may be considered as terminating near to and only a little