man then lived in the rudest possible condition of savagery.  He has, little by little, through long centuries and millenniums of painful struggle, survived in made his weapons and his most effective tools for the time being would be a good criterion to go by, because these weapons and tools enabled him to conquer not only the wild beasts around him and his fellow man also, but nature as well.  These materials are three in number.  They particularly apply to European archaeology, but, in a general way, to the archaeology of all continents.  The one is stone, which gave man material for the best cutting edge which he could make for very many millenniums of his existence.  After that, for a comparatively short period, he availed himself of bronze—­of the mixture of copper and tin called bronze—­an admixture giving a considerable degree of hardness and therefore allowing polish and edge making.  The bronze age was not long anywhere.  It was succeeded by that metal which, beyond all others, has been of signal utility to man—­iron.  We live in the iron age, and it is from iron in some of its forms and products that all our best weapons and materials for implements, etc., are derived.  We have, therefore, the ages of stone, of bronze and of iron.  These are the measures, from an artistic source, of the advancement of human culture; and they certainly bear a distinct relation to all man’s other conditions at the time.  A tribe which had never progressed beyond the stone age—­which had no better material for its weapons and implements than stone—­could never proceed beyond a very limited point of civilization.  Bronze or any metal which can be moulded, hammered and sharpened of course gives a nation vast superiority over one which uses stone only; and the value of iron and steel for the same purposes I need not dwell upon.

To be sure, we have here several measures; and it would seem more desirable, if we could, to obtain one single measure—­one single material or object of which we could say that the tribe that uses or does not use that to an equal degree is certainly lower or, in the other respects, higher than another; but I believe that there has been no single material which has been suggested as of sufficient use and value in this direction to serve as a criterion; but, yes!  I remember there was one and, on the whole, not a bad one.  It was suggested by Baron Liebig, the celebrated chemist, who said:  “If you wish a single material by which to judge of the amount of culture that any nation, or, for that matter, any individual, possesses, compared to another one, find out how much soap they use.  Nothing,” he said, “more than personal cleanliness and general cleanliness differentiates the cultured man from the savage;” and as for that purpose he probably had in view a soap, he recognized that as the one criterion.  It is not amiss, but open, also, to serious objections; because there are tribes who live in such conditions that they can get neither water nor soap; and the Arabs, distinctly clean, are not by any means at the highest pinnacle of civilization.