First, the multitude and the complexity of the circumstances that are necessary to lead men to make even the simplest invention render the concatenation of all of these conditions wholly independently on a second occasion in the highest degree improbable. Until very definite and conclusive evidence is forthcoming in any individual case it can safely be assumed that no ethnologically significant innovation in customs or beliefs has ever been made twice.

Those critics who have recently attempted to dispose of this claim by referring to the work of the Patent Office thereby display a singular lack of appreciation of the real point at issue. For the ethnological problem is concerned with different populations who are assumed not to share any common heritage of acquired knowledge, nor to have had any contact, direct or indirect, the one with the other. But the inventors who resort to the Patent Office are all of them persons supplied with information from the storehouse of our common civilization; and the inventions which they seek to protect from imitation by others are merely developments of the heritage of all civilized peoples. Even when similar inventions are made apparently independently under such circumstances, in most cases they can be explained by the fact that two investigators have followed up a line of advance which has been determined by the development of the common body of knowledge.

This general discussion suggests another factor in the working of the human mind.

When certain vital needs or the force of circumstances compel a man to embark upon a certain train of reasoning or invention the results to which his investigations lead depend upon a great many circumstances. Obviously the range of his knowledge and experience and the general ideas he has acquired from his fellows will play a large part in shaping his inferences. It is quite certain that even in the simplest problem of primitive physics or biology his attention will be directed only to some of, and not all, the factors involved, and that the limitations of his knowledge will permit him to form a wholly inadequate conception even of the few factors that have obtruded themselves upon his attention. But he may frame a working hypothesis in explanation of the factors he had appreciated, which may seem perfectly exhaustive and final, as well as logical and rational to him, but to those who come after him, with a wider knowledge of the properties of matter and the nature of living beings, and a wholly different attitude towards such problems, the primitive man's solution may seem merely a ludicrous travesty.

But once a tentative explanation of one group of phenomena has been made it is the method of science no less than the common tendency of the human mind to buttress this theory with analogies and fancied homologies. In other words the isolated facts are built up into a generalisation. It is important to remember that in most cases this mental process begins very early; so that the analogies play a very obtrusive part in the building up of theories. As a rule a multitude of such influences play a part consciously or unconsciously in shaping any belief. Hence the historian is faced with the difficulty, often quite insuperable, of ascertaining (among scores of factors that definitely played some part in the building up of a great generalization) the real foundation upon which the vast edifice has been erected. I refer to these elementary matters here for two reasons. First, because they are so often overlooked by ethnologists; and secondly, because in these pages I shall have to discuss a series of historical events in which a bewildering number of factors played their part. In sifting out a certain number of them, I want to make it clear that I do not pretend to have discovered more than a small minority of the most conspicuous threads in the complex texture of the fabric of early human thought.

Another fact that emerges from these elementary psychological considerations is the vital necessity of guarding against the misunderstandings necessarily involved in the use of words. In the course of long ages the originally simple connotation of the words used to denote many of our ideas has become enormously enriched with a meaning which in some degree reflects the chequered history of the expression of human aspirations. Many writers who in discussing ancient peoples make use of such terms, for example, as "soul," "religion," and "gods," without stripping them of the accretions of complex symbolism that have collected around them within more recent times, become involved in difficulty and misunderstanding.

For example, the use of the terms "soul" or "soul-substance" in much of the literature relating to early or relatively primitive people is fruitful of misunderstanding. For it is quite clear from the context that in many cases such people meant to imply nothing more than "life" or "vital principle," the absence of which from the body for any prolonged period means death. But to translate such a word simply as "life" is inadequate because all of these people had some theoretical views as to its identity with the "breath" or to its being in the nature of a material substance or essence. It is naturally impossible to find any one word or phrase in our own language to express the exact idea, for among every people there are varying shades of meaning which cannot adequately express the symbolism distinctive of each place and society. To meet this insuperable difficulty perhaps the term "vital essence" is open to least objection.

In my last Rylands lecture[11] I sketched in rough outline a tentative explanation of the world-wide dispersal of the elements of the civilization that is now the heritage of the world at large, and referred to the part played by Ancient Egypt in the development of certain arts, customs, and beliefs. On the present occasion I propose to examine certain aspects of this process of development in greater detail, and to study the far-reaching influence exerted by the Egyptian practice of mummification, and the ideas that were suggested by it, in starting new trains of thought, in stimulating the invention of arts and crafts that were unknown before then, and in shaping the complex body of customs and beliefs that were the outcome of these potent intellectual ferments.

In speaking of the relationship of the practice of mummification to the development of civilization, however, I have in mind not merely the influence it exerted upon the moulding of culture, but also the part played by the trend of philosophy in the world at large in determining the Egyptian's conceptions of the wider significance of embalming, and the reaction of these effects upon the current doctrines of the meaning of natural phenomena.

No doubt it will be asked at the outset, what possible connexion can there be between the practice of so fantastic and gruesome an art as the embalming of the dead and the building up of civilization? Is it conceivable that the course of the development of the arts and crafts, the customs and beliefs, and the social and political organizations—in fact any of the essential elements of civilization—has been deflected a hair's breadth to the right or left as the outcome, directly or indirectly, of such a practice?