THE ROYAL INSTITCTION OF GREAT BRITAIN. 217 



witli every circumstance wliicli can liave any relation to their causes. The error 

 of some of the ancient schools consisted principally in want of sufficient precau- 

 tion in this respect; for although Bacon is with great justice considered as the 

 author of the most coiTcct method of induction, yet, according to his own state- 

 ment, it was chiefly the guarded and gradual application of the mode of argu- 

 ment that he labored to introduce. lie remarks that the Aristotelians, from a 

 hasty observation of a few concurring facts, proceeded immediately to deduce 

 universal principles of science and fundamental 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 inipiiry. Of such an error we may easily find a 

 familiar instance. We observe that, in general, heavy bodies fall to the ground, 

 unless they are supported ; it was therefore concluded that all heav}^ bodies tend 

 downwards; and since flame was most freipiently seen to rise upwards, it was 

 therefore inferred that flame was naturally and absolutely light. Had suflicient 

 precaution been employed in observing the effects of fluids on falling and on 

 floating bodies, in examining the relations of flame to the circumambient atmo- 

 sphere, and in ascertaining the specific gravit}' of the air at different tempera- 

 tures, 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 phenomenon: 



" See with what force yon river's crystal stream 

 Resists the weight of many a massive 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 flaiiie has weight, though highly rare. 

 Nor mounts but when compelled by heavier air." 



"It may br proper to notice here those axioms which are denominated by 'New- 

 ton rules of philosophizing, although it must be' confessed that they render us 

 very little immediate assistance in our investigations. The first is that 'no more 

 causes are to be admitted as existing in nature than are at once true and sufficient 

 for explaining the phenomena to be considered;' the second, therefore effects 

 of the same kind are to be attributed, as far as possible, to the same causes ;' 

 thirdly, ' those qualities of bodies which cannot be increased nor diminished, 

 and which are found in all bodies within the reach of our experiments, are to be 

 considered as general qualities of all bodies existing;' fourthly, 'in experi- 

 mental philosoph}', propositions collected by induction from phenomena are to be 

 esteemed either accurately or very nearly true, notwithstanding any contrary 

 hypothesis, until other phenomena occur b}^ which they may either be corrected 

 or confuted.' 



"As an illustration of the remark that these axioms, though strictly true, are of 

 little real utility in assisting oiu* investigations, I shall give an instance from the 

 subject of electricity. Supposing that we wish to determine whether or no the 

 electric fluid has weight, we are to inquire whether or no gravitation is one of 

 those properties whicli are described in tlie third rule, and whether that rule will 

 authorize us to apply it to the electric fluid as one of those qualities of bodies, 

 which cannot be increased or diminished, Avhich are found in all bodies within 

 the reach of our experiments, and which are therefore to be considered as general 

 qualities of all bodies existing. Now, it appears to be, in the first [)lace, uncer- 

 tain whether or no the increase and diminution of gravity, from a change of dis- 

 tance, is strictly compatible with th(^ terms of the definition ; and in tlK> second 

 place, we are equally at a loss to decide whether or no the electric fluid can with 



