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J() LECTURE I.

want of sufficient precaution in this respect; for although Bacon is, withgreat justice, considered 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. lieremarks, that the Aristotelians, from a hasty observation of a few concurringfacts, .proceeded immediately to deduce universal principles of science, andfundamental laws of nature, and then derived from these, by their syllogisms,all the particular cases, which ought to have been made intermediate steps inthe inquiry. Of such .an error we may easily find a familiar instance. Weobserve, that, in general, heavy bodies fall to the ground unless they are sup-ported; it was therefore concluded that all heavy bodies tend downwards:and since flame was most frequently seen to rise upwards, it was inferred thatflame was naturally and absolutely light, llad sufficient precaution been em-ployed in observing the effects of fluids on falling and on floating bodies, inexamining the relations of flame to the circumambient atmosphere, and in as-certaining the specific gravity of the air at different temperatures, it wouldreadily have been discovered, that the greater weight of the colder air was thecause of the ascent of the flame; flame being less heavy than air, hut yethaving no positive tendency to ascend. And accordingly the Epicureans ,whose arguments, as far as they related to matter and motion, were oftenmore accurate than those of their cotemporaries, had corrected this error; forwe find in the second book of Lucretius a very just explanation of the pheno-menon.

“ See with what force yon river’s crystal streamResists the rveight 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 ascendNo 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 byNewton rules of philosophizing; although it must be confessed that theyrender us very little immediate assistance in our investigations. The first is,