4 ESSENTIALS OF BIOLOGY 



necessary. We can easily recognize organisms and we can always 

 be sure that a thing which we investigate is, or is not, alive. 

 There are very few cases in the history of science where life 

 was asserted of something that was not alive and in those cases 

 the error was quickly detected. Artifacts can also be recognized, 

 and here again it has not often happened that things fabricated 

 by organisms have been mistaken for inanimate things and vice 

 versa. Artifacts are lifeless things, but it is convenient to separate 

 them from those other inanimate things that we consider here. 

 In artifacts ** life has gone over into its products." 



2. ON THE STATUS OF NATURAL THINGS 



Natural things have what we shall call " status " in relation 

 to the passage of nature. 



2a. The Passage of Nature. Nature, meaning all that we 

 can observe and measure, continually changes and ** passes." 

 The great natural events, or changes, or phenomena, are the 

 radiation of the stars and the partially-known changes in the 

 interiors of the stars that maintain that radiation. The most 

 familiar natural phenomenon that we know is the shining of the 

 sun, the radiational energy of which is the cause of most of the 

 things that happen on the earth. Less familiar are the great 

 secular and cyclical changes in the earth itself, whereby moun- 

 tain ranges are built up and become eroded away. These changes, 

 in so far as they are not due to the sun's radiation, come from 

 the original heat and other energy of the earth-interior and these 

 came from the sun when the planet, earth, was formed. Thus 

 the great universal phenomena are seen in the radiation of the 

 stars, of which our sun is one. 



The movements of the stars and planets are only physical 

 changes in a restricted sense. These movements through space 

 are impressive ones, but they do not involve the expenditure of 

 energy — that is, no work is done in maintaining them. (This 

 statement is not strictly true, as w^e may see by considering 

 tidal friction, but nevertheless we may here neglect the very 

 small energy-changes implied.) 



Thus the sun and stars are to be regarded as reservoirs of 

 energy. It will be seen from Section 89 that these energy- 

 stores are being expended. The quantities of energy involved 



