Popular Science Monthly 



317 



the sparking-surfaces are made, and also 

 upon the freedom with which air is 

 admitted to the gap. Copper plates 

 which are not provided with airtight 

 gaskets soon become so thickly covered 

 with oxides or compounds including 

 nitrogen that gap action grows irregular; 

 it is therefore desirable to exclude air 

 from such instruments. When silver 

 surfaces are used, the oxidization is not 

 so rapid, and it is not necessary to take 

 such precautions. 



The drawing, which is taken from 1916 

 patent No. 1,171,598, issued to L. De- 

 Forest, shows a method which has been 

 found very useful for making quenched- 

 gaps airtight. The structure comprises 

 the usual plates 4, piled upon each other 

 and clamped by means of screw 16 into 

 containing frame 13. Electrical con- 

 nection is made through the wires 18 

 which are connected to the clamping- 

 heads 15. The novelty claimed for the 

 present patenc consists in the use, 

 between the individual plates of the 

 quenched-gap, of washers consisting of 

 soft compressible varnished or inipreg- 

 nated fabric. When this material is 

 clamped between the plates it effectually 

 prevents the entrance of air, and so 

 limits the formation of oxides upon the 

 surfaces of the plates. Further air- 

 tightness may be secured by filling the 

 space between the peripheral rims of the 

 plates with a compound such as paraffin 

 or beeswax, as shown at 10. 



In building quenched-gaps of airtight 

 construction, care must be taken that the 

 normal cooling of the gap is not greatly 

 reduced by prevention of ventilation. 

 Also, in using compressible gaskets, the 

 screw 16 must be carefully adjusted in 

 order that the plates be not forced into 

 accidental contact. If the necessary 

 precautions are taken to insure per- 

 manence of separation of the plates, an 

 airtight gap is likely to require cleaning 

 much less frequently than one in which 

 oxidization is permitted to progress 

 freely. 



Such an airtight quenched spark gap 

 is especially useful on ships at sea and 

 at any land stations which would be 

 effected by the rapid action of salt air 

 upon the material of the gap where it is 

 heated by the spark. 



In such a case a gap of this type will 

 not only work more efficiently but will 

 wear considerably longer. 



Spark Sender for Sustained 

 Wireless Waves 



THE drawing shows a transmitter 

 described in U. S. Patent 1,166,892, 

 issued in 1 91 6 to R. A. Fessenden. The 

 high-voltage direct current dynamo A 

 charges the outer plates of the condenser 



B, through the resistance or impedance 



C. The condenser discharges through 

 the oscillatory circuit formed by the 

 adjustable inductances in wires D and 

 E, and the rotating spark-gap F. 

 This gap consists of a stationary elec- 



nil 



r-mj^ \ — '^-^WWWV 



Fessenden's method for coupling the os- 

 cillatory circuit with that of the aerial 



trode placed near to a disk which 

 revolves at high speeds; the inventor 

 suggests that the relative movement of 

 the two sparking points may be as high 

 as 12 miles a minute. The construction 

 may involve two rotating disks, or some 

 other mechanical form which will operate 

 at very great speeds and so prevent the 

 formation of any ark in the gap. In 

 such an arrangement, the specification 

 states, continuous and regular discharges 

 are produced and sustained, or practically 

 sustained waves are generated at high 

 efficiency. 



The mode of coupling to the antenna- 

 to-ground circuit through the internal 

 plates G, H of the sending condenser 

 possesses some interest. This is equiva- 

 lent in many ways to the static couple 

 transmitters which have recently been 

 tried in connection with various types of 

 ark and spark generators. In order to 

 secure good transfer of oscillating current 

 energy from closed to open circuit it is 

 necessary that the radiating circuit 

 be in tune with the local circuit formed 

 by the plates of B and the inductance 

 in the lead wires D, E. This is 

 accomplished by the usual insertion of 

 variable inductance and capacity in the 

 antenna circuit. 



