78 WHAT IS SCIENCE? 



But expressions, or the ijleas contained in them, may 

 be more acceptable and more satisfactory, on grounds 

 other than their familiarity ; and all explanations do 

 not consist of a reduction of the less to the more familiar. 

 Indeed it would seem that the explanations which, in 

 the view of the man in the street, it is the business of 

 science to offer do not involve familiar ideas at all. Thus 

 we may expect our scientific acquaintances to explain 

 to us why our water-pipes burst during a frost or why 

 paint becomes dirty sooner in a room lit by gas than in 

 one lit by electricity. We shall be told in reply that the 

 bursting of the pipes is due to the expansion of water 

 when it is converted into ice, and the blackening of the 

 paint to the combination of the white pigment with 

 sulphur present in coal-gas to form compounds that are 

 dark, and not white, in colour. Now in these instances, 

 the ideas involved in the explanation are probably less, 

 and not more, familiar than those that they are used to 

 explain. Many more people know that water-pipes burst 

 during a frost than know that water (unlike most liquids) 

 expands when it freezes ; and many more know that 

 their paint goes black than know that lead carbonate 

 (one of the commonest white pigments) is converted by 

 sulphur into black lead sulphide. 



Why then do we regard our questions as answered ? 

 Why do we feel that, when we have received them, the 

 matter is better understood, and our ideas on it clearer 

 and more satisfactory ? The reason is that the events 

 and changes have been explained by being shown to be 

 particular examples of a general law. Water always 

 expands when it freezes, although it does not always burst 

 household pipes ; for it may not be contained in pipes or 

 in any closed vessel. And lead carbonate always reacts 

 with sulphur in the form present in coal-gas, even if it is 

 not being used as a pigment. We feel that our experience 

 is no longer peculiar and mysterious ; it is only one 



