ANALYSIS OF THE IONOSPHERE 



471 



Bureau of Standards and the Carnegie Institution. Automatically 

 sending out the signals ten times in a second, and changing the fre- 

 quency by (on the average) 1600 cycles between each signal and the 

 next while the photographic film is moved a tiny bit from left to right, 

 this "multi-frequency apparatus" traces the ih',f) curve over the 



0.516 



2 3 4 5 6 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 7 — Characteristic {h',f) curves obtained with the multi-frequency apparatus; 

 sun low in sky, Fi crinkle missing. (Carnegie Institution of Washington) 



frequency-range between 0.516 mc. and 16 mc. in fifteen minutes, 

 and then goes right back and does it over and over again. Figures 6, 

 7 and 8 show individual curves thus automatically taken, and Fig. 15 

 a sequence of them spanning several hours of the day. 



In Fig. 6 are curves with crinkles in the /^-branch, similar to those 

 of Figs. 4 and 5. In Fig. 7, however, the crinkle is missing, and the 



