Decembee lOj 1915] 



SCIENCE 



815 



the so-called "practical" wireless engineer 

 has made in the direction of overcoming the 

 interference of the "static" consisted in in- 

 creasing continually the power applied at 

 the signalling station so as to make the sig- 

 nals at their arrival at the receiving sta- 

 tion stronger than the signals made there by 

 the static. These attempts failed, as they 

 should. The static is an act of God and his 

 acts can not be neutralized by brute force. 

 The machinery of nature will not interfere 

 with the machinery constructed by man if 

 man puts a sufficient amount of intelligence 

 into his machine. In other words, the prac- 

 tise of the wireless art needs more pure sci- 

 ence before it can expect to overcome the 

 very serious interferences due to the action 

 of the static. Ordinary electrical tuning 

 will not do, because every system which is 

 highly selective through ordinary tuning 

 is also highly sonorous. Every tap of the 

 static will cause it to vibrate and it will 

 vibrate in the same way as when it is under 

 the action of the signalling waves. We must 

 look for some other form of electrical selec- 

 tivity, and this is the last point which I wish 

 to bring before you now, but only very 

 briefly. 



The eye sees a very narrow strip of wave 

 frequencies which are sent from a radiating 

 body ; the ear hears a very narrow strip of 

 wave frequencies which vibrating bodies can 

 send out. Physiological optics and physio- 

 logical acoustics deal with these remark- 

 able facts. Now the reason v\'hy the eye is 

 blind and the ear is deaf to an enormous 

 range of frequencies is certainly not due to 

 anything like ordinary selectivity produced 

 by tuning. The selectivity must be due to 

 something else. Physicists see resonance 

 and tuning wherever they find selectivity, 

 but it is high time to formulate broader 

 views. 



Fifteen years ago I published several in- 

 vestigations which deal with electrical mo- 



tion in sectional wave conductors. One of 

 these resulted in the now well-known loaded 

 telephone line. I regret that the technical 

 importance of this invention, by attracting 

 too much attention, has overshadowed com- 

 pletely the full meaning of the general 

 mathematical theory which underlies it. This 

 theory says that sectional wave conductors 

 can be made which will absorb almost com- 

 pletely all waves above or below a certain 

 small range of frequencies, and the selectiv- 

 ity thus obtained has nothing to do with 

 ordinary electrical tuning. In other words, 

 the selectivity of the eye and of the ear can 

 be imitated by coarse structures like sec- 

 tional wave conductors. Electrical pulses 

 produced by the static are for the most 

 part very short and their action is equiva- 

 lent to the action of highly damped elec- 

 trical oscillations of very high pitch. This 

 action can be entirely absorbed so that no 

 part of it reaches the receiving apparatus 

 of a wireless receiving station if between the 

 antenna and the receiving apparatus a sec- 

 tional wave conductor is employed which 

 will not transmit electrical waves of a fre- 

 quency higher than a given range of fre- 

 quencies. The station becomes then an ear 

 which is quite sensitive for frequencies 

 which are in the vicinity of the signalling 

 frequency, but which is stone deaf to fre- 

 quencies which are considerably beyond 

 this range as most static disturbances are. 

 Similarly, a sectional wave conductor can be 

 constructed which is quite responsive to fre- 

 quencies in the vicinity of the signalling 

 frequency, but absorbs almost completely 

 everything below tliis range. My theoretical 

 and experimental investigations encourage 

 me in the belief that a perfect barrier has 

 been' found against disturbances due to the 

 so-called static, and that the distances of 

 uninterrupted wireless telegraphy and tele- 

 phony will be very greatly increased. 



M. I. PUPIN 



