I JOSEPH PRIESTLEY 27 



promulgated, without challenge, by persons occu- 

 l^ying the highest positions in the State Church. 



I must confess that what interests me most 

 about Priestley's materialism, is the evidence that 

 he saw dimly the seed of destruction which such 

 materialism carries within its own bosom. In the 

 course of his reading for his " History of Dis- 

 coveries relating to Vision, Light, and Colours," 

 he had come upon the speculations of Boscovich 

 and Michell, and had been led to admit the suffi- 

 ciently obvious truth that our knowledge of matter 

 is a knowledge of its properties; and that of its 

 substance — if it have a substance — we know noth- 

 ing. And this led to the further admission that, 

 so far as we can know, there may be no difference 

 between the substance of matter and the substance 

 of spirit C' Disquisitions," p. 16). A step farther 

 would have shown Priestley that his material- 

 ism was, essentially, very little different from the 

 Idealism of his contemporary, the Bishop of Cloyne. 



As Priestley's philosophy is mainly a clear state- 

 ment of the views of the deeper thinkers of his day, 

 so are his political conceptions based upon those of 

 Locke. Locke's aphorism that "the end of gov- 

 ernment is the good of mankind," is thus expanded 

 by Priestley: — 



" It must necessarily be understood, therefore, whether it 

 be expressed or not, that all people live in society for their 

 mutual advantage ; so that the good and happiness of the 



