THE NEW LOGICS. 175 



all the properties of phosphorus except its melting- 

 point, melt, as it does, at 44° centigrade." It has been 

 objected that this law is not verifiable, for if we came 

 to verify that two bodies resembling phosphorus melt 

 one at 44° and the other at 50° centigrade, we could 

 always say that there is, no doubt, besides the melting- 

 point, some other property in which they dififer. 



This was not exactly what I meant to say, and I 

 should have written : " all bodies which possess such 

 and such properties in finite number (namely, the 

 properties of phosphorus given in chemistry books, 

 with the exception of its melting-point) melt at 44° 

 centigrade." 



In order to make still clearer the difference between 

 the case of the straight line and that of phosphorus, 

 I will make one more remark. The straight line has 

 several more or less imperfect images in nature, the 

 chief of which are rays of light and the axis of 

 rotation of a solid body. Assuming that we ascertain 

 that the ray of light does not satisfy Euclid's postulate 

 (by showing, for instance, that a star has a negative 

 parallax), what shall we do? Shall we conclude that, 

 as a straight line is by definition the trajectory of 

 light, it does not satisfy the definition, or, on the 

 contrary, that, as a straight line by definition satisfies 

 the postulate, the ray of light is not rectilineal ? 



Certainly we are free to adopt either definition, 

 and, consequently, either conclusion. But it would be 

 foolish to adopt the former, because the ray of light 

 probably satisfies in a most imperfect way not only 

 Euclid's [postulate but the other properties of the 

 straight line ; because, while it deviates from the 

 Euclidian straight, it deviates none the less from the 



