52 WHAT IS SCIENCE? 



But it is much more doubtful whether it is only, or 

 even mainly, such sequences which are studied in the 

 establishment of laws. Indeed, some of the examples 

 of laws that have been quoted already seem to state 

 relations which are not sequences. For instance, we 

 spoke of the law of the association of the properties of 

 steel or of a magnet. But properties are not events which 

 follow each other. It is not necessary, in order to prove 

 that a substance is steel, always to observe that it is 

 attracted by a magnet before it is observed that it will 

 rust in damp air ; there is no time-relation of any kind 

 between the two properties. The properties of a single 

 substance, the invariable association of which is asserted 

 by the law of that substance, are something quite inde- 

 pendent of the times at which they are observed. They 

 differ completely in this matter from events which are 

 related to each other as cause and effect. 



And there are scientific laws of another kind which are 

 not concerned with the invariable sequences that con- 

 stitute cause and effect, namely, numerical laws, of 

 which we shall have much to say later. Important 

 examples of such laws are those which state that one 

 magnitude is proportional to another. For instance, 

 Ohm's Law states that the electric current through a 

 conductor is proportional to the electrical pressure 

 between its ends, so that if the pressure is doubled, the 

 current is doubled. Here, again, there is no time-relation 

 involved ; the law states something about numbers 

 and the size of the things that they represent ; there is 

 no idea of one thing being before or after another. 



But, if there are so many and such important laws 

 which are obviously not concerned with cause and 

 effect, how did the idea ever arise that the establishment 

 of causes and effects was the sole or main purpose of 

 scientific laws ? In respect of the first example which 

 has been quoted, that of laws which state the properties 



