178 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



and grooves were cut in it longitudinally. It was found in this way 

 that practical transmission could be accomplished with 10,000 breaks 

 per second. It is believed now that this number is unnecessarily 

 high, possibly owing to the fact that it was impossible to cut the 

 grooves on the cylinder without producing ridges. The lower limit 

 may be fixed in another way. 



Electrical circuits met with in actual working have resistance, self - 

 inductance capacity, and leakance. Heaviside gave the differential 

 equations for the pressure and current over such circuits when 

 alternating voltages were applied, but no method of solution being 

 known, the mathematical treatment of such circuits was restricted 

 to cases where one of the constants was neglected, until Dr. A. E. 

 Kennelly in a masterly series of papers gave the complete solution. 



The results were immediately found applicable to a great variety 

 of problems, such as the transmission of signals through cables and 

 of telephonic speech through various types of circuits. 



In this way Doctor Kennelly '^ by comparing the results obtained 

 by Dr. Hammond V. Hayes ^ in practical telephonic transmission 

 over loaded lines with the theoretical values of the current for dif- 

 ferent harmonics showed that harmonics above 2,000 per second could 

 be neglected for telephonic transmission. 



The writer has never succeeded in obtaining good talking with 

 such a low frequency, but under favorable conditions fairly satis- 

 factory speech may be obtained with 5,000 interruptions per second. 

 For really good transmission, however, the radiation must be prac- 

 tically continuous, for if the spark frequency is less than 20,000 

 per second there is a disagreeable high pitch note in the telephone, 

 not noticeable perhaps at first but apt to become annoying with use. 

 The most satisfactory way is, of course, to use a source of sustained 

 oscillations. 



It fortunately happens that for wireless telephonic purposes it is 

 inadvisable to use a wave frequency of less than 25,000 per second, 

 on account of the difficulty in radiating energy with low frequencies. 



The receiver must, of course, be continuously responsive. If, for 

 example, it had to be tapped back in order to restore it to the 

 responsive condition, speech could not be transmitted. 



It must also give indications proportional to the energy received 

 or the character of the speech will be distorted. 



It must also respond with sufficient rapidity. If, for example, it 

 takes a thousandth of a second to restore itself to its original resist- 



o Kennelly, " Distribntion of i)ressnre and current over alternating-current 

 circuits," Harvard Engineering Journal, 1906, p. 43. 



^ Hayes, " Jjoaded telephone lines in practice," Transactions International 

 Electrical Congress, St, Louis, vol. 3. 



