XLVIII ROYAL SOCIETY OF CANADA 



and scattering it internally. It would appear also that for about 70 

 years after Newton's death nobody repeated his experiments or else tha 

 glass was bad, and the lines were not discovered until AVoUaston's time. 

 His paper was published in the Philosophical Transactions in 1803. 



Although quotations from the "Opticks" are not very uncommon it 

 would lappear from the next instance I shall produce that the book is 

 difficult of access. It would be a benefit to science if some wealthy 

 American University were to reprint so famous a work, a model of clear- 

 ness and accurate experiment. 



Newton and Herbert Spencer. 



This third instance occurred a few years earlier, when Herbert 

 Spencer was led to put his opinions directly in opposition to those of 

 Newton, in Natural Philosophy itself, through a mistake about the 

 meaning of a word in the Principia, which would have been avoided 

 had the " Opticks " l)een consulted. Newton calls the laws of motion 

 " axioms " ; Spencer, evidently having in his mind the ordinary use of 

 the word axiom in the modern editions of Euclid, as meaning a self- 

 evident proposition, insisted that Newton employed it in this sense. 



An inspiriting discussion in print followed wliich ended by Spencer's 

 acknowledging that Newton attached a different meaning to the word. 

 The proof! was obtained from Newton's letters, and in the whole 

 discussion no reference was made to the " Opticks." Yet a glance at tlie 

 book would have ended the debate. Newton begins it with definitions 

 and axioms. The "axioms" are the Laws of "Eeflexion and Eefraction," 

 and these, as some school boys kriow, are established hj experiment solely. 

 Spencer says that Newton " gives the word axiom a sense widely unlike 

 the sense in which it is usually accepted," implying perhaps some 

 censure on Newton. If " usually " means usually at the present day, 

 Spencer is correct. But is it possible he can have forgotten that a word 

 may change its meaning with the lapse of time? A very brief inquiry 

 would have shown that Newton used the word accurately both in the 

 " Opticks " and the " Principia." No deeper research is required than 

 turning over the leaves of Liddell and Scott to find that it was employed 

 by Aristotle to signify "that which is assumed as a basis oî demonstra- 

 tion ;" for " assumption " in short, or " postulate ;" the root idea being 

 that of wo'rthiness, something worthy of acceptance without disputation. 

 Nor is Euclid responsible for the word, since he didn't use it and is thus 

 doubly free from the charge of calling his principle about parallel lines 

 " self-evident." 



The question arose in a controversy between Herbert Spencer and 

 Prof. Tait. The latter in his Thermodynamics asserts that Natural 



