454 



Tables 540 and 541 



TABLE 540. — Values of Dielectric Constant for Several Electrical Insulating 

 Materials at Radio-Frequencies 



Material 



Frequency, 



kc 



Measurements reported by- 

 2 3 



Glass 30 



Crown glass 230 



800 



Flint glass 500 



890 



Plate glass 500 



Cobalt glass 500 



Pyrex glass 30 



500 



Photographic glass 100 



1700 



Hard rubber 135 



210 

 1126 



Marble 44 



80-650 

 1400 



Mica 100-1000 



Laminated ) 



p heno !- c " 1000 



insulation I 

 Moulded | 



P heno !! c " 1000 



insulationj 



Wood (oak) 300 



425 



635 



1060 



(maple) 500 



(birch) 500 



(baywood) 870 



7.0 

 7.0 

 6.8 



7-3 



4.9 



30 

 3.o 



5-4-5-8 

 5-1-5-6 



3-2 

 3-3 

 3-3 

 3-3 

 4.4 



5-2 



5-i-7-9 a 



3- 

 9.2-11.7° 



5-8 : 8. 7 



5-0-7-4 

 4.7-7.0 



4-3-7-6 

 4.9-7.0 



6.7, 3.i b 

 6.5, 3-o b 



4.4 



3-8 



(1) Bairsto, G. E., Conductivity and dielectric constant of dielectrics for high-frequency oscillations. 

 Proc. Roy. Soc. London, A, 96, 363-382, Jan., 1920. (2) Hoch, E. T., Power losses in insulating ma- 

 terials. Bell System Tech. Journ., I, No. 2, Nov., 1922. (3) Decker, William C, Power losses in com- 

 mercial glasses. Electr. World, 89, 601-603, March 19, 1927. (4) Data from the Bureau of Standards. 



a Range of 9 samples of various chemical compositions reported. b After drying sample for 48 hours at 

 8o c C. '' Range of 10 samples of various kinds of marble. 



TABLE 541. — Absorption Factors for Radio Propagation 



For frequencies up to 1000 kc and transmission over sea water the semiempirical trans- 

 mission formulas of Austin-Cohen, Austin, Fuller, and Espenschied, Anderson and Bailey 

 take the form 



-ad 



F (fx volts/meter) = (377 /\)(hf/d) Vfl/sin 6 • e ^ 

 where the coefficient 377A//XJ represents the simple Hertzian radiation field over a per- 

 fectly conducting plane surface, the factor Vtf/sin d corrects the formula for the curvature 

 of the earth, and the factor e-a<^A x is the absorption factor, a the damping factor, and x 

 is determined experimentally, d, the distance from the transmitter, and X, the wave length, 

 both are measured in kilometers. The following tabulation completes the information con- 

 cerning these formulas. (See next page.) 



Smithsonian Tables 



