FIRST EDITION. XIX 



in its independent character, as a History, this book 

 may be found not altogether unworthy of the aim 

 which its title implies. 



It is impossible not to see that the writer of such 

 a history imposes upon himself a task of no ordinary 

 difficulty and delicacy ; since it is necessary for him 

 to pronounce a judgment upon the characters and 

 achievements of all the great physical philosophers of 

 all ages, and in all sciences. But the assumption 

 of this judicial position is so inevitably involved in 

 the functions of the historian (whatever be his sub- 

 ject), that he cannot justly be deemed presumptuous 

 on that account. It is true, that the historian of the 

 progress of science is required by his undertaking 

 to judge of the merits of men, in reference to subjects 

 which demand a far intenser and more methodical 

 study than the historian of practical, life gives to the 

 actions of which he treats ; and the general voice of 

 mankind, which may often serve as a guide, because 

 it rarely errs widely or permanently in its estimate 

 of those who are prominent in public life, is of little 

 value when it speaks of things belonging to the region 

 of exact science. But to balance these disadvan- 

 tages, and to enable us to judge of the characters who 

 must figure in our history, we may recollect that 

 we have before us, not the record only of their 

 actions, but the actions themselves ; for ,the acts of 

 a philosopher are his writings. We do not receive 

 his exploits on tradition, but by sight ; we do not 

 read of him, we read him. And if I may speak of 

 my own grounds of trust and encouragement in 

 venturing on such a task, I knew that my life had 



