104 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 5 



lying in different directions, at different times of day and different 

 seasons of the year. Preliminary observations had been made at the 

 Bureau of Standards in the summer and autumn of 1919, using a lower 

 pole, shorter collectors and less efhcient screening, so that the possible 

 errors of observation at that time were not much less than 10 degrees. 

 During this time a large number of observations were made on various 

 stations including New Brunswick, Annapolis, Nauen, Lyons, San 

 Juan and Darien, but in no case were any deviations of the wave front 

 from the vertical found which were greater than the estimated errors 

 of observation. The work with the final apparatus at Anacostia had 

 been in progress only a short time when it became necessary to remove 

 the pole as it was considered dangerous to the aviators at Boiling 

 Pield. 



Daylight observations 



The results obtained during this period are given below. While 

 they are not as extensive as would be desirable, they probably fix a 

 definite limit to the deviations of the wave front from the vertical for 

 the stations measured, under conditions of normal daylight reception. 

 A great number of measurements were made on the near-by stations, 

 New Brunswick and Annapolis, largely as a test of the accuracy of 

 the apparatus, as it was assumed that the wave front at these dis- 

 tances would be practically vertical. New Brunswick showed an 

 apparent bending forward of the wave front amounting to 3.1°, while 

 Annapolis showed an apparent bending back amounting to 2.2°. 

 These apparent deviations are considered as probably due to syste- 

 matic errors of the apparatus, depending apparently on the direction 

 of the horizontal axis. 



TABLE 1. Wave Front Angles, June, 1920 



Apparent Number Maximum 



Distance Wave angle of of sets of deviation of 



in nautical length in wave front observa- any set 



Station miles meters mean tions from mean 



New Brunswick 1.52 13,000 +3 .1« 44 +1 .4° 



Annapolis 29 17,200 —2.2° 14 +1.2° 



Nauen 3595 12,500 +3.4° 3 —0.4° 



San Diego 1974 15,200 —0.8° 1 +1.3° 



" The plus sign indicates a forward sloping wave front. 



The chief interest in the experiments was of course centered in 

 observations on stations at a great distance. A number of observa- 

 tions were made on Nauen of which the average is given in table 1. 

 It is seen that the deviation from the vertical is only slightly greater 

 than the estimated error. On one day measurements were also ob- 

 tained on San Diego. This observation is of especial interest because 



