58 THE PHYSICAL SCIENCES APPARENTLY UNKNOWN 



experienced in the sensible effects upon each other of the ma- 

 terials with which they operated, and empirically acquainted 

 with their properties ; but being, at the same time, entirely ig- 

 norant of their intimate nature and relations. In other words, 

 that the Science of nature was unknown to them. They had ob- 

 served, for example, pursuing the illustration just given, that 

 a dead body became putrid unless its moisture was expelled ; 

 but they were ignorant that the cause which rendered this 

 precaution necessary, was the tendency of water to promote 

 the chemical action of the constituents of the body upon each 

 other, by favouring their assumption of the liquid form, and 

 also by suffering decomposition, and yielding one of its con- 

 stituents (the oxygen) to them. They had found that the ex- 

 clusion of the atmosphere was necessary, to effect the long- 

 continued preservation of organic bodies ; but they did not 

 know the ground of this necessity, in the circumstance, that 

 the atmosphere, by the oxygen it contains, and the water 

 which is diffused through it, is the great natural agent of de- 

 composition. They knew that variations of temperature were 

 unfavourable to the preservation of animal matter in its natu- 

 ral form, but they had no knowledge, that the cause of this 

 lay in the fact, that the chemical affinities of the elements of 

 such matter are greatly influenced by the heat to which it may 

 be exposed, and that the changes of texture induced by al- 

 ternations of temperature, permit a more complete operation of 

 those affinities. They appear, in short, to have pursued the 

 arts in a manner altogether empirical and without principles ; 

 a conclusion which is confirmed by what Diodorus Siculus 

 and other historians have related of their mode of practising 

 medicine, and some branches of the arts also, which are all, in 

 our own times, intimately connected with scientific knowledge. 

 It is probable, indeed, that this was at once originally the 

 cause, and eventually, in an aggravated form, the consequence 

 also, of the division of the Egyptian people into six hereditary 

 ranks, each of which was confined, from generation to gene- 

 ration, to the exercise of the same general function in society 

 as had been originally performed by it, whilst the individuals 

 of whom it was composed, and their posterity, were equally 

 restricted to the particular occupations of their respective pro- 

 genitors. Whatever knowledge might be possessed by each 

 class, was thus entirely traditive, and confined to itself, and 

 never contributed to form a common stock of information. 

 For arts pursued without principles, and without some degree 

 of scientific knowledge of the materials and agents employed, 

 though they might readily be transmitted from one manipula- 

 tor to another, as workmen at the present day instruct ap- 



