RETROSPECT AND PROSPECT 



these sequences of events. Let us, for example, take 

 the familiar and fundamental observation that any 

 unsupported object, having what we term weight, in- 

 variably falls directly towards the centre of the earth. 

 We express this fact in terms of a so-called law of grav- 

 itation, and every one, consciously or unconsciously, 

 gives full deference to this law. So firmly convinced 

 are we that the gravitation pull is a cause that works 

 with absolute, unvarying uniformity that we should 

 regard it as a miracle were any heavy body to disre- 

 gard the law of gravitation and rise into the air when 

 not impelled by some other force of which we have 

 knowledge. Thanks to Newton, we know that this 

 force of gravitation is not at all confined to the earth, 

 but affects the whole universe, so that every two bits of 

 matter, regardless of location, pull at each other with 

 a force proportionate to their mass and inversely as 

 the square of their distance. 



Were this so-called law of gravitation to cease to 

 operate, the entire plan of our universe would be sadly 

 disarranged. The earth, for example, and the other 

 planets would leave their elliptical orbits and hurtle 

 away on a tangential course. We should soon be be- 

 yond the reach of the sun's beneficent influence; an 

 arctic chill would pervade polar and tropical regions 

 alike, and the term of man's existence would come 

 suddenly to a close. Here, then, is a force at once the 

 most comprehensible and most important from a 

 human stand-point that can be conceived ; yet it can- 

 not be too often repeated, we know nothing whatever 

 as to the nature of this force. We do not know that 

 there may not be other starlike clusters beyond our 



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