Mr. G. Marconi. On the Effect of Daylight [June 10, 



It has been shown also by Gerosa, Finzi, and others that the effect 

 of alternating currents or high-frequency electrical oscillations acting 

 upon iron is to reduce considerably the effects of magnetic hysteresis, 

 causing the metal to respond much more readily to any influence which 

 tends to alter its magnetic condition. The effect of electrical oscilla- 

 tions probably is to bring about a momentary release of the molecules 

 of iron from the constraint (or viscosity) in which they are ordinarily 

 held, diminishing their retentiveness, and consequently decreasing the 

 lag in the magnetic variation taking place in the iron. 



I therefore anticipated that the group of electrical waves emitted by 

 each spark of a Hertzian radiator would, if caused to act upon a piece 

 of iron which is being subjected at the same time to a slowly varying 

 magnetic force, produce sudden variations in its magnetic hysteresis, 

 which variations would produce others of a sudden or jerky nature in 

 its magnetic condition. In other words, the magnetisation of the iron, 

 instead of slowly following the variations of the magnetic force 

 applied, would at each spark of the transmitter suddenly diminish its 

 magnetic lag caused by hysteresis. 



. These jerks in the magnetic condition of the iron would, I thought, 

 cause induced currents in a coil of wire of strength sufficient to allow 

 the signals transmitted to be detected intelligibly on a telephone, or 

 perhaps even read on a galvanometer. 



The tests to which I have referred above confirm my belief that the 

 magnetic detector can be substituted for the coherer for the purposes 

 of long-distance space telegraphy. 



"A Note on the Effect of Daylight upon the Propagation of 

 Electromagnetic Impulses over Long Distances." By 

 G. Marconi, M.I.E.E. Communicated by Dr. J. A. Fleming, 

 F.K.S. Eeceived June 10,— Bead June 12, 1902. 



During some long-distance space telegraphy tests carried out 

 towards the end of February last between a transmitting station 

 situated at Poldhu, on the coast of Cornwall, and a receiving station 

 on board the U.S. s.s. " Philadelphia " travelling from Southampton to 

 New York, I had the opportunity of noticing for the first time in my 

 experience, considerable differences in the distances at which it was 

 possible to detect the received oscillations during daylight, as com- 

 pared with the distances at which the effects could be obtained at 

 night. 



Before describing the results obtained, it may be useful if I give a 



