Conclusion
To end a book about such a subject as the UFO phenomenon with the word 'conclusion' is surely something of a bad joke for which I should really apologise. If there is any conclusion, it is simply that there is no conclusion. We may conclude the book, but we reach no conclusion as to the nature of the subject of the book.
Yet perhaps the solution of the problem is within reach today. Perhaps the masses of data on sightings, the numerous interviews with witnesses and the hours spent researching by dedicated men and women have already laid bare the solution but we are all looking at the evidence in the wrong way to see it. Perhaps, someday soon, someone will look at the data collected in a fresh way and see the solution in a flash. This has happened many times in the history of science and in the history of problem-solving generally, and we can hope that the UFO problem will prove to be another example.
One of the great problems encountered so far by researchers has been the 'ink blot' nature of the phenomenon, i.e. there has always been a tendency to project one's own preconceptions (especially subconscious preconceptions) into the data and then read out what one subconsciously expects or wishes, in the manner of a psychologist's patient reading a picture into an ink blot.
Perhaps this accounts, at last in part, for the constant irrationality and absurdity which the phenomenon seems to display - absurd sightings, absurd patterns, absurd hypotheses. The subconscious love absurdity and, we are told by psychologists and hypnotists, it is opened to suggestion by a confrontation with the absurd - a confrontation which confuses the normal thinking process of the rational consciousness just long enough to let the absurdities of the subconscious filter through.
Then, what greater absurdity is there than contacteeism and the beliefs which it expounds - beliefs which, if our argument has been correct, come from the most stygian depths of the subconscious and permeate the collective mind far beyond the company of the contactees themselves?
How many interpretations of UFO sightings have been moulded by these beliefs, without the witness ever realising it?
Yet, as we have seen, certain constants do keep recurring in UFO reports and it seems pretty clear that some of these betray genuine regularities in the phenomenon itself, rather than psychological constants in the reporting of that phenomenon.
Thus, perhaps the best way in which to conclude this book is to list a number of features which have occurred over and over again in the reports of independent witnesses and which may, therefore, be assumed to point towards some intrinsic property(ies) of the UFO phenomenon. This list will, doubtless, not be exhaustive but at least it will enable some sort of a model of the UFO to be built up and tested against the major hypotheses.
In what follows, these various features of the UFO phenomenon will be listed and briefly discussed, with the list and comparisons with the chief hypotheses then being summarised in tabular form.
(1) They are generally nocturnal. This could suggest either a natural phenomenon occurring more readily under nocturnal conditions, or a secret craft of man-made origin, or a secret craft of extraterrestrial origin. The similarity with psychic or paraphysical phenomena which are also, traditionally, associated with night, should also be noted.
(2) They are mainly yellow to reddish in colour. This is also the colour range most frequently reported in cases of ball lightning, suggesting some association of the mechanisms operating. This association may be one of identity, but it could also imply that certain types of craft (secret military, or extraterrestrial or from another time) are able to surround themselves with an envelope of ionised air, from which most of the luminous effect arises.
(3) They display a strong tendency to follow the contours of the land, sometimes stopping over bodies of water. This could be explained if the UFOs were very sensitive to the change in the electrical potential of the Earth's electric field. It is well known that considerable electrical variations exist between different altitudes in the lower atmosphere, and if a craft was fitted with a device for measuring the exact potential of the atmosphere and the results of this reading were fed back to an automatic pilot, such a craft would, by keeping to a layer of constant electrical potential, hug the contours of the land exactly in the manner of UFOs.
Presumably, a natural phenomenon of electrical nature may be able to do this as well, but this feature of the UFO, if taken in isolation from all others, would seem best explained in terms of a terrestrial robot aircraft. A spacecraft from another planet is less likely, as such potential differences exist only in the lower atmosphere and the mere fact that the UFO can lock into them seems to imply close association with terrestrial conditions.
The ability of TT or PP to explain this feature is unknown, although it may be possible to explain much paranormal visual phenomena in electrical terms.
(4) They are frequently said to rotate, principally in a counterclockwise direction. The reason for this is unclear, although it may be relevant to mention that ball lightning is also said to rotate, but I do not know whether there is any preference for counter-clockwise rotation in this case.
(5) They sometimes leave physical traces. This suggests that the objects are solid, at least temporally, or that they are associated with a force sufficiently strong to be able to imitate the effects of a solid object.
(6) Sightings are usually fairly localised. Even spectacular UFOs are not, in general, reported by large numbers of witnesses over a wide area - in strong distinction to brilliant meteors or large, high-altitude balloons. This rather suggests either a vertical approach through the atmosphere or sudden appearance at or near ground level. With ETI the first alternative is possible, though dangerous because of the atmospheric friction involved. TT and PP seem on strongest ground with, perhaps, HA on weakest.
(7) Sudden appearances and disappearances are not uncommon. This seems, at face value, to explain point 6 and would appear to further strengthen the hands of TT and PP in explaining the localised nature of the phenomenon.
(8) High speeds and very rapid accelerations are sometimes reported. This is explained with difficulty by ETI (rapid accelerations would crush occupants, unless further ad hoc assumptions are made) and with even greater difficulty by HA and NP. TT and PP may be on better ground, although exactly how they would explain this phenomenon is unclear.
(9) Sounds (usually a hum or swish) are sometimes reported, especially, it would seem, from those objects of more solid appearance. Probably explicable by all theories.
(10) Wide variety of shapes and sizes of objects noted. Probably explicable on all theories, although TT and PP seem to be on the best ground.
(11) Low-level sightings seem to avoid places of high population density. Superficially, this looks like a secret operation and, therefore, would seem to support HA in the sense that the artefact in question could be a secret military aircraft.
(12) Sometimes the phenomenon seems to zero in on a particular person, who may suffer considerable parapsychic experiences. PP seems the most obvious explanation of this, but it is possible that the psychic effects could be secondary and that the basic phenomenon may be explicable in other ways.
(13) Entities which appear to be living creatures are often observed in conjunction with the phenomenon. ETI is not on as safe ground as might first appear in explaining this aspect of the phenomenon. TT and PP appear stronger, but HA and MP fail, unless (contrary to the reported data) 'creature' sightings are to be explained as simple hallucinations.
(14) Entities, like the objects themselves, are sometimes said to be luminous. This appears best suited to TT and PP (with PP in the stronger position), but it may be possible to explain such sightings by HA or NP if the entities are explained away as mistaken interpretations of other luminous effects.
(15) Two-way contact between human beings and these entities is quite widely alleged but such information as is passed along in these contacts is always rather puerile. The similarity between these contacts and spiritualism strongly suggests an explanation within the field of PP. ETI and to some extent TT are virtually parodied by this aspect of the phenomenon.
Most contacts involve either telepathy or the use of a loudspeaker and radio set - however, even this latter set of equipment seems to have a habit of answering questions (allegedly from the depths of space) in a shorter time than would be allowed by radio transmission and reception and, at times, is even alleged to answer the sender's thoughts. Hallucination or psycho-kinesis must be involved here, and it is reasonable to conclude that the 'message' comes from the contactee's own subconscious mind.
(16) Objects and their alleged entities appear to exhibit intelligence, though mostly of a puerile, playful and - at times - even mischievous nature. Again, this aspect of the phenomenon seems to parody ETI and possibly TT, and cannot, therefore, be adequately explained by these theories. PP appears to be the strongest contender as an explanation of this aspect of the UFO phenomenon.
The table below indicates that the particular aspect of the phenomenon listed could probably be explained in terms of the theory under whose heading it appears. The symbol / ? indicates that this is possibly so, X ? that it probably is not so and X that the aspect of the UFO phenomenon being considered is unlikely to be explicable in terms of the indicated theory.

Where? appears, the situation is considered too uncertain to make any definite statement.
Of course, the above table is very far from the last word on the matter. For one thing, it depends upon the assumption that the actual hypotheses themselves make sense, i.e. that it is not total nonsense to speak about life on other planets, about time travel or about paraphysical phenomena.
Furthermore, it rests on the fact that we have some (more or less vague) notion about what extraterrestrial life-forms would look like and how they would behave; it assumes that we not merely accept the possibility of time travel, but also that we have some notion about how it could be effected (even if this notion does not extend beyond thinking in terms of materialisations and de-materialisations), and it assumes that we have reached the conclusion that the science of paraphysics really does have a bona fide subject matter - a conclusion which not all para-physicists would readily endorse.
We then say, in effect, 'If we can meaningfully speak about these hypotheses, we may then test to see if they are able to explain the various aspects of the UFO phenomenon.'
This is the most that the table can hope to accomplish. Rather, it should be looked upon as an example of how to test UFO hypotheses once more is known about both the phenomenon itself and the reliability of the different hypotheses, than any real conclusion to our present knowledge.