178 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



followers of Hertz and Righi had been stopped in their progress 

 toward short waves about 1 cm., or two-fifths of an inch, in length. 

 In some experiments still in progress at the Nela Research Labo- 

 oratory of the National Lamp Works, at Cleveland, the writers, by 

 devising new and improved instruments and methods of experi- 

 mentation, have succeeded in generating and working with electric 

 waves as short as 0.220 mm., or one one-hundredth of an inch — waves 

 considerably shorter than Ruben's and von Baeyer's 0.324 mm., heat 

 waves. 



DESCRIPTION OF SENDING AND RECEIVING APPARATUS 



The arrangement of apparatus used in the new experiments is 

 shown in Plate 1. The Hertzian oscillator or sender is contained in 

 a brass box, O. The oscillator is a point source, and the diverging 

 pencil of electric wave radiation emerging from it is formed into 

 a parallel beam by a lens of paraffin wax. At R 2 , with a similar 

 lens in front of it, is a check receiver. Waves emitted by the sender 

 first fall on the reflecting screen, G, which is usually of ebonite, and 

 are partially reflected into the check receiver. The remaining por- 

 tion passes through the screen and falls upon the reflecting echelon 

 analyzer, a flight of exactly equal brass steps, S. From the face of 

 the echelon, the beam of electric waves is reflected to the main re- 

 ceiver, R v A motor-driven vacuum pump for exhausting the two 

 receivers is seen in the background. The check receiver, R 2 , serves 

 simply as a control on the intensity of the beam emitted by the 

 oscillator, so that any erratic changes of intensity of the emitted 

 radiation may be recognized and corrected for. 



The oscillator. — In a sectional diagram of the oscillator or send- 

 ing apparatus shown in Figure 1, in which interior parts appear very 

 much magnified, B is a brass case containing kerosene. T 1 and T 2 

 are glass tubes in which very small cylinders of tungsten, H 1 and H 2 , 

 are sealed. These tungsten cylinders, separated by a short spark 

 gap in kerosene, form the Hertzian doublet which emits the short 

 wave radiation. High potential leads, V x and V 2 , from an induc- 

 tion coil charge H x and H 2 by leakage across air gaps, G x and G,, 

 until H x and H 2 build up a sufficiently high potential difference to 

 break down the kerosene insulation in the spark gap, G. The en- 

 suing electrical oscillations between H x and H 2 are the source of the 

 electric waves. Radiation emerging from the oscillator case passes 

 through the thin circular mica window, W, falls on the paraffin lens, 

 P, and is formed into a parallel beam. M is a concave metal mirror 

 behind the doublet to reenforce the issuing beam by reflecting the 

 backward emission of the oscillator. For simplicity many necessary 

 details, such as fine adjustments for regulating the spark gap, etc.. 



