PREFACE. 7 



intricately turned and twisted:*' through all which we are 

 only to be conducted by the uncertain light of the senses, 

 that sometimes shines^ and sometimes hides its head ; and by 

 collections of experiments and particular facts, in which no 

 guides can be trusted, as wanting direction themselves, and 

 adding to the errors of the rest. In this melancholy state 

 of things, one might be apt to despair both of the under- 

 standing left to itself, and of all fortuitous helps ; as of a 

 state irremediable by the utmost efforts of the human 

 genius, or the often-repeated chance of trial. The only cluo \ > ^ 

 and method is to^begin^all anew, and direct our steps in a | f^ 

 certain order, from the very first perceptions of the senses, j 

 Yet I must not be understood to say that nothing has been I 

 done in former ages, for the ancients have shown themselves 

 worthy of admiration in everything which concerned either 

 wit or abstract reflection ; but, as in former ages, when men 

 at sea, directing their course solely by the observation of the 

 stars, might coast along the shores of the continent, but 

 could not trust themselves to the wide ocean, or discover new 

 worlds, until the use of the compass was knoAvn: even so 

 the present discoveries referring to matters immediately 

 under the jurisdiction of the senses, are such as might easily 

 result from experience and discussion ; but before we can 

 enter the remote and hidden parts of nature, it is requisite 

 that a better and more perfect application of the human 

 mind should be introduced. This, however, is not to be 

 understood as if nothing had been effected by the immense 

 labours of so many past ages; as the ancients have per- 

 formed surprisingly in subjects that required abstract medi- 

 tation, and force of genius. But as navigation was imperfect 

 before the use of the compass, so will many secrets of nature 

 and art remain undiscovered, without a more perfect know- 

 ledge of the understanding, its uses, and Avays of working. 



For our own part, from an earnest desire of truth, we 

 have committed ourselves to doubtful, difficult, and solitary 

 ways ; and relying on the Divine assistance, have supported 

 Qur niinds against the vehemence of opinions, our own in- 

 ternal doubts and scruples, and the darkness and fantastic 



« By wreaths and knots, is understood the apparent comphcation of 

 causes, and the superaddition of properties not essential to things ; aa 

 light to heat, yellowness to gold, pellucidity to glass, &c. Shaw. 



