THE SELECTION OF FACTS. 21 



to look for the cases in which the rule stands the best 

 chance of being found in fault. This is one of many 

 reasons for the interest of astronomical facts and of 

 geological ages. By making long excursions in 

 space or in time, we may find our ordinary rules 

 completely upset, and these great upsettings will give 

 us a clearer view and better comprehension of such 

 small changes as may occur nearer us, in the small 

 corner of the world in which we are called to live and 

 move. We shall know this corner better for the 

 journey we have taken into distant lands where we 

 had no concern. 



But what we must aim at is not so much to ascertain 

 resemblances and differences, as to discover similarities 

 hidden under apparent discrepancies. The individual 

 rules appear at first discordant, but on looking closer 

 we can generally detect a resemblance ; though differ- 

 ing in matter, they approximate in form and in the 

 order of their parts. When we examine them from 

 this point of view, we shall see them widen and tend 

 to embrace everything. This is what gives a value to 

 certain facts that come to complete a whole, and 

 show that it is the faithful image of other known 

 wholes. 



I cannot dwell further on this point, but these few 

 words will suffice to show that the scientist does not 

 make a random selection of the facts to be observed. 

 He does not count lady-birds, as Tolstoi says, because 

 the number of these insects, interesting as they are, is 

 subject to capricious variations. He tries to condense 

 a great deal of experience and a great deal of thought 

 into a small volume, and that is why a little book on 

 physics contains so many past experiments, and a 



