Finally, to give a last form to the mechanical theory of heat, the conception of flying atoms or molecules was introduced, and a number of neat generalisations were deduced from dynamical considerations. Of course it was inevitable, having once started with a mechanical theory, that one should arrive at the Atom some time or other--and (from what has already been said) it was also inevitable that the result should be unsatisfactory. It is sufficient to say that the molecular theory of heat is _not_ in accordance with facts. Such things as the law of Charles and the law of Boyle, which according to it should be strictly accurate and of general application, are known to be true only over a most limited range. This failure of the theory may be said to arise partly from its being pursued by the statistical method; but if, on the other hand, we were to try and follow out the individual movement of each molecule we should be landed in a problem far exceeding in complexity the wildest flights of Astronomy, and should have exchanged for the original difficulty about "temperature" a difficulty far greater. The result of all this has been that notwithstanding the talk about energy and atoms, Science has sadly to confess that it can still give no valid meaning to the word temperature: the unknown thing is still unknown, the independent existence round the corner still escapes us. By the very effort to arrive at something independent of human sensation, Science has, in a roundabout way, arrived at an absurdity. When the man said he was cold, his statement--deplorably vague as it certainly was--had some meaning; he was describing his feelings, or possibly he had seen some snow or some ice on the road; but when, in the endeavour to leave out the human and to say something absolute, Science declared that the temperature was thirty degrees, it committed itself to a remark which possibly was exact in form, but to which it has never given and never can give any definite meaning.[30] Similarly with other generalities of Science: the "law" of the Conservation of Energy, the "law" of the Survival of the Fittest--the more you think about them the less possible is it to give any really intelligible sense to them. The very word Fittest really begs the question which is under consideration, and the whole Conservation law is merely an attenuation of the already much attenuated "law" of Gravitation. The Chemical Elements themselves are nothing but the projection on the external world of concepts consisting of three or four attributes each: they are not more real, but very much less real than the individual objects which they are supposed to account for; and their "elementary" character is merely fictional. It probably is in fact as absurd to speak of pure carbon or pure gold, as of a pure monkey or a pure dog. There are no such things, except as they may be arrived at by arbitrary definition and the method of ignorance.