We must now consider rather more definitely than we have hitherto done whether there is any thing in the hypothesis to conflict with those established conclusions of scientists which are the nearest approach we have to absolute certainties. I think we shall find not only that there is no such conflict but that there are here and there distinct indications that the higher space ideas may some day find applications in the exegesis of even the most strictly physical sciences. These indications are admittedly very nebulous at present, it may be that they are all illusory and as will appear later they cannot _all_ lead to anything, for some are mutually exclusive. I do not propose to express any very definite opinions on their comparative values but shall simply state them and leave it to my readers to decide what they are worth. It must be remembered throughout that we cannot expect to find any very definite indications of the existence of higher space as a reality for the simple reason that physical science is concerned solely with those phenomena of matter and force which are "_ex hypothesi_" essentially three-dimensional. It is worth noting at the outset that physical scientists have evinced no especial hostility to the concept of the fourth dimension, as such, however much they may have opposed to the more definitely Psychic researches which I, personally, believe to be closely associated with it. Lord Kelvin, for instance, saw in it nothing repugnant to scientific thought and professed himself quite willing to adopt it should such a course seem to be indicated by the evidence. Another distinguished physicist has gone so far as to evolve a theory of "ether squirts" from the direction of the fourth dimension in connection with the ultimate constitution of matter. Again M. Poincaré the distinguished French Physicist has said "The characteristic property of space, that of having three dimensions is only ... a property residing, so to speak, in human intelligence." Mathematical physicists also find that certain experimental anomalies are resolved if they refer phenomena to four interchangeable axes involving homogeneous co-ordinates instead of to three space axes and one time axis. If this is not dealing in four-dimensional space it is first cousin to it. M. Poincaré also pointed out that the postulates of Euclid are not experimentally verifiable facts and as a matter of fact much work has been done in the elaboration of non-Euclidean geometries. This is too mathematical a subject to be dealt with in detail here, but I can indicate the general drift of it, so far as it is relevant to the present discussion by means of the time honoured analogy of the two-dimensional world.