]() LECTURE I. 



want of sufficient precaution in this respect; for although Bacon is, with 

 great justice, consiclered as the author of the most correct method of induc- 

 tion, yet, according to his own statement, it was chiefly the guarded and gra- 

 dual application of the mode of argument, that he laboured to introduce. He 

 remarks, that the Aristotelians, from a hasty observation of a few concurring 

 facts, proceeded immediately to deduce universal principles of science, and 

 fimdamental laws of nature, and then derived from these, by their syllogisms, 

 all the particular cases, which ought to have been made intermediate steps in 

 the inquiry. Of such an error we may easily find a familiar instance. Wd 

 observe, that, in general, heavy bodies fall to the ground unless tliey are Sjup- 

 ported; it was therefore concluded that all heavy bodies tend downwards: 

 and since flame was most frequently seen to rise upwards, it was inferred that 

 flame was naturally and absolutely light. Had sufficient precaution been em- 

 ployed in observing the effects of fluids on falling and on floating bodies, in 

 examining the relations of flame to the circumambient atmosphere, and in as- 

 certaining the specific gravity of the air at different temperatures, it would 

 readily have been discovered, that the greater weight of the colder air was the 

 cause of the ascent of the flame ; flame being less heavy than air, but yet 

 having no positive tendency to ascend. And accordingly the Epicureans, 

 whose arguments, as far as they related to matter and motion, were often, 

 more accurate than those of their cotemporaries, had corrected this error; for 

 we find in the second book of Lucretius a very just explanation of the pheno- 

 menon. , 



■" See with what force yon river's crystal stream 



Resists the weight of many a massy beam. 



To sink the wood the more we vainly toil, 



The higher it rebounds, with swift recoil. 



Yet that the beam would of itself ascend 



No man will rashly venture to contend. 



Thus too the flame has weight, though highly rare, 



Nor mounts but when compelled by heavier air." 



It may be proper to notice here those axioms which are denominated by 

 Newton rules of philosophizing; although it must be confessed that they 

 render us very little immediate assistance in our investigations. The first is, 



