294 . THE FOUNDATIONS OF ZOOLOGY 



phenomenon ? Simply that in all human experience all stones 

 have fallen to the ground under these conditions, and that we 

 have not the smallest reason for believing that any stone so cir- 

 cumstanced will not fall to the ground, and that we have, on the 

 contrary, every reason to believe that it will so fall. It is very 

 convenient to indicate that all the conditions of belief have been 

 fulfilled in this case, by calling the statement that the unsup- 

 ported stone will fall to the ground a law of nature. But when, 

 as commonly happens, we change will into must, we introduce an 

 idea of necessity which most assuredly does not lie in the observed 

 facts, and has no warranty that I can discover elsewhere. For 

 my part I utterly repudiate and anathematize the intruder. Fact 

 I know; and Law I know; but what is this Necessity save an 

 empty shadow of my own mind's throwing ? " 1 



"Attraction," says Berkeley, "cannot produce, and in that 

 sense account for the phenomena, being itself one of the phenom- 

 ena produced and to be accounted for." 



If words like these mean anything, they mean that they who 

 think the movements of the mechanism of nature necessary utterly 

 misapprehend the value and significance of natural knowledge. 

 They mean that belief that the automatic clock is self-sustaining 

 and must go finds no support in the teachings of science; except 

 so far as it may be supported by something in our own nature. 



If man were a pure intellect, the intensity of our confidence 

 in gravitation might be identical with its logical value ; but as a 

 man is a ponderable body and not a pure intellect, serious bodily 

 harm, or even death, may follow failure to respond to that part of 

 the order of nature which we formulate as the law of gravitation. 



The actions of most terrestrial animals large enough to be 

 injured by a fall are so adjusted to this order that the practical 

 value of their responses does not bear any exact relation to their 

 opportunities for acquiring experience. When a mud-turtle or a 

 marine crab is put on a table, it may walk over the edge without 

 hesitation ; but a land-crab, on reaching the edge, hunts for a safe 

 place to climb down, and if forced to go over, clings to the table, 

 or else drops with caution after preparation. Nestling birds, 



i "Physical Basis of Life," 1868. 



