Biographical Memoir ofDr Priestley. 217 



had made use of them without perceiving them, how often he 

 possessed new substances without distinguishing them; and 

 never does he conceal the erroneous views which sometimes di- 

 rected him, and the fallacy of which he discovered only by ex- 

 periment. These avowals did honour to his modesty, without 

 disarming jealousy. Those whose views and modes of proce- 

 dure had never furnished them with any discovery, called him 

 a mere maker of experiments, without method and without ob- 

 ject. There is no wonder, said they, that, among so many trials 

 and combinations, there should be some productive of fortunate 

 results. 



But those who possessed the true spirit of philosophy were 

 far from being the dupes of these interested criticisms. They 

 knew by how many efforts those happy ideas are always elicited, 

 which lead to and regulate all the others ; and the men who, 

 after having had the good fortune to make great discoveries, 

 have taken pleasure in increasing our admiration by the beau- 

 tiful light in which they have placed them, entertain no hostile 

 feelings towards those who, like Priestley, have preferred ac- 

 celerating our enjoyment, by presenting their discoveries as ra- 

 pidly as they have made them, and by ingenuously tracing all 

 the windings by which they were led to them. This was the 

 effect of his manner of writing. His book is not like a regu- 

 larly constructed edifice, a series of theorems deduced succes- 

 sively one from another, as they might have been conceived 

 in the eternal mind : it is the simple journal of his thoughts, 

 in all the disorder of their succession. We see in it a man who 

 at first walks groping in a dark night — who spies the smallest 

 glimmerings — who seeks to bring them together and reflect 

 them — whom fallacious and transient lights sometimes mislead, 

 but who at length arrives at a rich and extensive region. 



Should we have been grieved if the great masters of the human 

 race, the Archimedeses and Newtons, had thus made us the con- 

 fidants of their genius ? Newton, on being asked how he had ar- 

 rived at his great discoveries, replied, by thinking long upon them. 

 What pleasure would it have afforded us to have been made ac- 

 quainted with the long series of thoughts from which at length 

 sprung that grand conception of Newton — that thought, which 

 is, so to speak, even at the present day, the soul of all his suc- 

 cessors ! His books have made us acquainted with the powers of 



