UNDER THE APPLE-TREES 
always essentially the same. Gravity is the ruling 
force. But among chemical bodies a new force ap- 
pears; chemical affinity is here the determining fac- 
tor. The law of probability plays a secondary part. 
Spontaneous combustion, for instance, is a molecu- 
lar accident only in a limited sense. The antecedent 
conditions may be in a measure accidental, but the 
chemical reactions that bring about the rise of tem- 
perature to the point of combustion are not acci- 
dental; they inhere in the constitution of the ele. 
ments. Life may be of spontaneous and fortuitous 
origin in the same sense; not a mere chance happen- 
ing among unrelated bodies, but the continuation of 
long-antecedent conditions brought about by that 
mysterious force we call chemical attraction. This 
force, as it were, gives the elements eyes, and hands, 
and feet, and power of choice, and determines the 
line of their activities. Liquid water, without which 
life could not exist, was contingent upon the chemi- 
cal union in fixed properties of the two gases, oxygen 
and hydrogen; accident may have played a part in 
the meeting of those two gases, but, once met, under 
the proper conditions, water was bound to appear. 
The chemical union of oxygen and silica, which 
forms so large a part of the earth’s surface, was pre- 
determined by the nature of the substances, but the 
forms of the landscape and the size and the shape 
of the continents were not in the same sense prede- 
termined. An entirely different disposition of the 
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