“…The most interesting feature of the disturbances mentioned above is without doubt the strong ionization in the lower ionosphere on 7 July, showing up in the very strong absorption of HF radio waves, and the fact that no magnetic effects could be observed. Such an effect was observed the first time in connection with the large solar flare of 23 February 1956 (according to SHAPLEY andROB-ERTS, 1957) and several reports were published on it (BAILEY, 1957;LIED, 1957;SHAPLEY and ROBERTS, 1957, and others).…”