To: Lt. Colonel Subj: Anomalous

consider the most probable explanation of green fireballs to be the one given in the first two paragraphs of the letter and are quoted from my letter of 1950, February 20, to Dr. E. H. Wells, Chief Atmos- pheric Physics Laboratory, Air Directorate for Geophysical Research. The last two paragraphs quoted below will summarize my recommendations concerning the green fireball problem:

"As a preliminary to setting down the proposed recommendations which you requested, I have very carefully reviewed all available fireball data (observers' reports, transit measurements, calculated real paths, etc.) covering incidents from those of December 5, 1948 to the extraordinary incident of February 7, 1950, which has been under intensive investigation for the last two weeks. As a result of this comprehensive review, particularly as it relates to the in- cident of February 7, 1950, I feel compelled to write you in some- what different terms concerning my views on the proposed fireball project than I had in mind when we last discussed this matter. In brief, I have come to the conclusion that, on the basis of the evidence now available to me, I would not be justified in recommend- ing a fireball project. In my opinion, this evidence proves conclu- sively that the fireballs reported on Fall into one of two categories: Those of the first category (the majority) are meteorite falls of unusual, but certainly not of impossible, magnitude, frequency and other characteristics; those of the second category (the minority) are U. S. guided missiles undergoing tests in the neighborhoods of the sensitive installations they are designed to defend. This interpretation of the latter category is the one that I proposed in answer to a question raised by Dr. Teller at the first Los Alamos conference on 17 March 1950. It is not taken seriously then and I doubt that it will be taken seriously at the present time. However, even if my interpretation of the unconventional fireballs is the correct one, it is obvious that those in position to confirm it should refuse to do so."

"Only one other point need be stressed, namely, that if I am wrong in interpreting the guided missiles as U. S. origin, then certainly intensive, systematic investigation of these objects should not be delayed until the termination of the present academic year. Recent international developments compel me to stress the imperative necessity of immediate investigation of the unconvention- al green fireballs, in case you are in possession of information proving that they are not U. S. missiles."

"If such an immediate investigation were to be undertaken, I would recommend that Dr. Fred L. Whipple, of Harvard College Obser- vatory, be placed in charge of the photographic side of the inves-

be placed in charge of the spectroscopic phase of the investigation;