HERTZIAN M'AYE WIRELESS TELEGRAPHY. 36g 



therefore for any given voltage varies as the capacity, and therefore 

 as the length of the transmitting aerial. If, therefore, the trans- 

 mitting and receiving aerial have the same length, the minimum 

 energy varies as the square of the electromotive force in the receiving 

 aerial, and therefore as the fourth power of the length of either aerial, 

 since the electromotive force varies as the product of the lengths of 

 the aerials. Hence when the distance between the aerials is constant, 

 the minimum working energy varies as the fourth power of the height 

 of either aerial, but when the lengths of the aerials are constant, the 

 energy caught up by the receiving aerial must vary inversely as the 

 square of the distance D between the aerials. Hence if we call e this 

 minimum working energy, e must vary as 1/D^ when L is constant, 

 or as L^ when D is constant, and since e is a constant quantity for 

 any given arrangements of receiver and transmitter, it follows that 

 when the height of aerial and distance vary, the ratio L*/D- is con- 

 stant, or, in other words, D- varies as L* or D varies as L^, i. e., dis- 

 tance varies as the square of the height of the aerial, which is Mar- 

 coni's Law. The curve therefore connecting height of aerial with 

 sending distance for given arrangements is a portion of a parabola. 



Otherwise, the law may be stated in the form L = a.-[/r), where « 

 is a numerical coefficient. If L and D are both measured in meters, 

 then for recent Marconi apparatus as used on ships a = 0.15, roughly. 

 (See a report on experiments made for the Italian navy 1900-1901, 

 by Captain Quintino Bonomo — 'Telegrafia senza tili,' Home, 1902.) 



This law, however, must not be used without discretion. After Mr. 

 Marconi had transmitted signals across the British Channel, some 

 people, forgetting that a little knowledge is a dangerous thing, pre- 

 dicted that aerials a thousand feet in height would be required to 

 signal across the Atlantic, but Mr. Marconi has made such improve- 

 ments of late years in the receiving arrangements that he has been 

 able to receive signals over three thousand miles in 1903, with aerials 

 only thirty-three per cent, longer than those wdiich, in 1899, he em- 

 ployed to cover twenty miles across the British Channel. 



We turn, in the next place, to the consideration of those devices for 

 putting more power into the aerial than can be achieved when the 

 aerial itself is simply employed as the reservoir of energy. Professor 

 Braun of Strasburg, in 1899, described a method for doing this by 

 inducino: oscillations in the aerial bv means of an oscillation trans- 

 former, these oscillations being set up by the discharges from a Leyden 

 jar or battery of Leyden jars, which formed the reservoir of energy. 

 The induction coil is employed to produce a rapidly intermittent series 

 of electrical oscillations in the primary coil of an oscillation trans- 

 former by the discharge through it of a Leyden jar. Mr. Marconi 



VOL. Lxiir. — 24. 



