2.34 



NA TURE 



[April 22, 1909 



granting the possibility of tliis, whether such a powerful 

 radiator would not interfere with the working of all other 

 wireless stations which might be established on shore or 

 ships within the sphere of influence of the long-distance 

 sender. 



What so often occurs in most pioneer work has repeated 

 itself in the case of long-distance wireless telegraphy — the 

 anticipated obstacles and difficulties were either imaginary 

 or else easily surmountable ; but in their place unexpected 

 barriers manifested themselves, and my efforts and those of 



FIC.2 



my collaborators have been mainly directed to the solution 

 of problems presented by difficulties which were not antici- 

 pated when the tests over long distances were first 

 initiated. 



In January, igoi, wireless communication was estab- 

 lished between St. Catherine's Point in the Isle of Wight 

 and Lizard in Cornwall, over a distance of iS6 miles. 

 The height of these stations above the sea-level did not 

 exceed 300 feet (100 metres), whereas 

 to clear the curvature of the earth a 

 height of more than a mile at each 

 end would have been necessary. 



The result of these tests went far 

 to convince me that electric waves pro- 

 duced in the manner I had adopted 

 were able to make their way round 

 the curvature of the earth, and that 

 therefore it was not likely that this 

 factor would constitute a barrier to 

 the transmission of waves over greater 

 distances. At this time I had 

 achieved a considerable measure of 

 success, by means of syntonic or 

 tuning devices, in preventing mutual 

 interference between stations, and 

 Prof. Fleming described, in a letter to 

 the Times, dated October 4, 1900, 

 the results obtained, and which he 

 and others had witnessed (Journ. .Soc. 

 Arts, xlix.. No. 2530, 1901). The 

 principle on which the transmitters 

 and receivers at St. Catherine's Point 

 and the Lizard were worked is shown 

 iii Figs. 3 and 4. 



At the transmitting end a condenser, 

 usually taking the form of a battery 

 of Leyden jars, had one terminal con- 

 nected to one spark-ball of an induc- 

 tion coil or transformer and the other 



to the primary circuit of an oscillation transformer. The 

 opposite terminal of this transformer circuit was joined to 

 the second spark-ball. The condenser was charged to the 

 potential necessary to produce a suitable spark bv means 

 of an induction coil. The secondary circuit of the oscilla- 

 tion transformer was inserted between the vertical conductor, 

 or aerial wire, and earth, and an adjustable inductance coil 

 included in the circuit. 



The circuits, consisting of the oscillating circuit and 

 radiating circuit, were more or less closely " coupled " by 

 varying the distance between the primary and secondary of 



NO. 2060, VOL. 80] 



the oscillation transformer. By the adjustment of the in- 

 ductance inserted between the elevated conductor and 

 earth, and by the variation of the capacity of the primary 

 circuit of the oscillation transformer, the two circuits of 

 the transmitter could be brought into resonance, a con- 

 dition which I first found was absolutely necessary in order 

 to obtain efficient radiation. 



The receiver consisted also of a vertical conductor or 

 aerial connected to earth through the primary of an oscilla- 

 tion transformer, the secondary of which included a con- 

 denser and a coherer, or other suitable detector, it being 

 necessary that the circuit containing the aerial and the 

 circuit containing the detector should be in resonance with 

 each other, and also in tune with the periodicity of the 

 oscillations transmitted from the sending station. 



The energy employed to signal over a distance of 186 

 miles could be brought as low as 150 watts, and even less 

 if a higher or larger aerial had been used. 



The facility with which distances of more than 100 miles 

 could be covered prior to 1900, and the success of the 

 methods for preventing mutual interferences (Journ. Soc. 

 .•^rts, xlix.. No. 2530, 1901), led me to advise that two 

 large power stations be constructed, one in Cornwall and 

 the other in North America, in order to test whether it 

 was possible to transmit messages across the Atlantic 

 Ocean. 



I have often been asked why I did not first endeavour 

 to establish commercial communication between places 

 situated at a shorter distance. The answer is very simple. 

 The cables which connect England to the Continent, and 

 between most Continental nations, are Government-owned, 

 and these Governments would not, and will not, allow 

 the establishment of any system, wireless or otherwise, 

 which might in any way tamper with the revenue derived 

 from these cables. 



As regards Transatlantic communication, however, the 

 conditions were different. There was no law either here, 

 in Canada, or in the United States to impede the working 

 of wireless telegraphy across the Atlantic. 



FIG.4. 



A further potent reason, moreover, an economical reason, 

 prompted me to attempt communication with America. 

 Notwithstanding the cost of high-power stations, I am 

 convinced that it is more profitable to transmit messages 

 at 6d. a word to .\nierica than at, say, Jd. a word across 

 the Channel, and that the economical advantage of wire- 

 less over cables and land-lines increases instead of diminish- 

 ing with the distance. 



A site suitable for a long-distance station was chosen at 

 Poldhu, in Cornwall, and here in 1900 work was com- 

 menced in earnest — work in which I was ably assisted by 



