i6o POPULAR. SCIENCE MONTHLY. 



irregular signs, which, however, sometimes spell out words in the 

 Morse code. He noted that these disturbances are more frequent in 

 summer and autumn than in winter and spring, and in the neighbor- 

 hood of high mountains more than in the open sea. In settled weather, 

 if present, they reach their maximum between 8 and 10 p. m., and 

 frequently last during the whole of the night, with a minimum of dis- 

 turbance between 9 a. m. and 1 p. m. Another important matter noted 

 by Captain Jackson is the shorter distance at which signals can usually 

 be received when any electrical disturbances are present in the atmos- 

 phere, compared with the distance at which they can be received when 

 none are present. This reduction in signaling distance may vary 

 from 20 to 70 per cent, of that obtainable in fine weather. It does not 

 in any way decrease with the number of lightning flashes, l)ut rather the 

 reverse, the loss in signaling distance generally preceding the first 

 indications on the instrument of the approaching electrical disturbance. 

 It is clear that these observations fit in very well with the theory out- 

 lined above, viz., that the atmosphere when impregnated with free 

 electrons or negatively charged gaseous ions is more opaque to Hertzian 

 waves than when they are absent. Captain Jackson gives an instance 

 of ships whose normal signaling distance was 65 miles, failing to com- 

 municate at 22 miles when in the neighborhood of a region of electrical 

 disturbance. These effects in the case of wireless telegraphy have 

 their parallel in the disturbances caused to telegraphy with wires by 

 earth currents and magnetic storms. 



Another effect wliich he states reduces the usual maximum signaling 

 distance is the presence of material particles held in suspension by the 

 water spherules in moist atmosphere. The effect has been noticed in 

 the Mediterranean Sea when the sirocco wind is blowing. This is a 

 moist wind conveying dust and salt particles from the African coast. 

 A considerable reduction in signaling distance is produced by its 

 advent. 



Another interesting observation due to Captain Jackson is the ex- 

 istence of certain zones of weak signals. Thus, for instance, two ships 

 at a certain distance may be communicating well; if their distance 

 increases, the signaling falls off, but is improved again at a still greater 

 distance. He advances an ingenious theory to show that this fact may 

 be due to the interference between two sets of waves sent out by the 

 transmitter having different wave lengths. 



Finally, in the paper referred to, he emphasizes the well-known 

 fact that long distance signaling can only be accomplished by the aid 

 of an aerial wire and a 'good earth. ' Summing up his results, he con- 

 cludes: (1) That intervening land of any kind reduces the practical 

 signaling distance between two ships or stations, compared with that 



