abstracts: radiotelegraphy 359 



common use it was deemed advisable for the Bureau of Standards to 

 investigate the effect of rotation of the gas-filled lamp on current and 

 candlepower, hoping to derive a practical method of photometry free 

 from the errors due to rotation. 



During the investigation extreme care was exercised in the control 

 and measurement of speed of rotation, and the precision photometer 

 was used in making the photometric measurements. It was found that 

 there was for every lamp investigated a speed at which both current 

 and mean horizontal candlepower had the same values, respectively, as 

 when the lamp was stationary, and that this speed had a value which 

 might be conveniently employed in practice, thus suggesting a practical 

 photometric method. It is pointed out, however, that owing to the 

 unequal distribution of bulb discoloration during the life of the gas- 

 filled lamp an integrating sphere should be used in measurements made 

 during life test. G. W. M. 



RADIOTELEGRAPHY.— The effect of imperfect dielectrics in the field 

 of a radiotele.gr aphic antenna. J. M. Miller, Bureau of Standards 

 Scientific Paper No. 269, pp. 129-136. 1916. 



It has been shown by the measurements of C. Fischer and L. W. 

 Austin that the curve which represents the variation of the resistance 

 of an antenna with the wave length of the oscilliation has two character- 

 istic features. Starting from the wave length corresponding to the fun- 

 damental of the antenna, the resistance of the antenna rapidly decreases 

 with increasing wave length and reaches a minimum. As the wave 

 length is still further increased the resistance rises again, but in a linear 

 manner. The initial decrease in resistance is explained by a decrease 

 in the so-called "radiation resistance." It has been difficult, however, 

 to account for the linear increase which takes place at the longer wave 

 lengths and it is the explanation of this feature that is here considered. 



Austin has explained this phenomenon as caused by dielectric absorp- 

 tion and has concluded that it takes place in the ground. Austin's 

 hypothesis with respect to dielectric absorption is confirmed but it is 

 found that the energy loss is not caused by the ground but by the pres- 

 ence of poor dielectrics in the field of the antenna. This conclusion is 

 based upon measurements of the resistance of an experimental antenna 

 constructed so as to eliminate poor dielectrics from its field and at 

 the same time to increase any effects which may be due to the ground. 

 The linear rise in its resistance at very long wave lengths (even at tele- 

 phone frequencies) was extremely small. It was then found that the 



