But--so the plain man is tempted to argue--we can tell quite well, because we can touch objects that we see, and discover that there is something hard and solid in the place from which the light-waves come. Or, again, we may find that there is something there which, though not solid, is very hot, and burns us when we try to touch it. We all feel that touch gives more evidence of “reality” than sight; ghosts and rainbows can be seen but not touched. One reason for this greater sense of reality is that our spatial relation to an object when we touch it with our finger-tips is given, and therefore an object does not give such different impressions of touch to different people as it does of sight. Another reason is that there are a number of objects that can be seen but not touched--reflections, smoke, mist, etc.--and that these objects are calculated to surprise the inexperienced. None of these facts, however, justify the plain man in supposing that touch makes him know real things as they are, though we are verbally forced to admit that it brings him into “contact” with them. We have seen on an earlier occasion how complex is the physical and physiological process leading from the object to the brain when we touch something; and we have seen that illusions of touch can be produced artificially. What we experience when we have a sensation of touch is, therefore, no more a revelation of the real nature of the object touched than what we experience when we look at it. As a matter of fact, if modern physics is to be believed, sight, prudently employed, gives us a more delicate knowledge concerning objects than touch can ever do. Touch, as compared with sight, is gross and massive. We can photograph the path of an individual electron. We perceive colours which indicate the changes happening in atoms. We can see faint stars even though the energy of the light that reaches us from them is inconceivably minute. Sight may deceive the unwary more than touch, but for accurate scientific knowledge it is incomparably superior to any of the other senses. It is chiefly through ideas derived from sight that physicists have been led to the modern conception of the atom as a centre from which radiations travel. We do not know what happens in the centre. The idea that there is a little hard lump there, which _is_ the electron or proton, is an illegitimate intrusion of common-sense notions derived from touch. For aught we know, the atom may consist entirely of the radiations which come out of it. It is useless to argue that radiations cannot come out of nothing. We know that they come, and they do not become any more really intelligible by being supposed to come out of a little lump.