NOVUM ORGANUM. 299 



Itaque tails circa hanc rem poterit esse Instantia Crucis. 

 Sumatur horologium ex iis quae moventur per ponclera plum- 

 bea, et aliud ex iis quae moventur per compressionem laminae 

 ferreae; atque vere probentur, ne alterum altero velocius sit 

 aut tardius ; deinde ponatur horologium illud movens per pon- 

 dera super fastigium alicujus templi altissimi, altero illo infra 

 detento ; et notetur diligenter si horologium in alto situm 

 tardius moveatur quam solebat, propter diminutam virtutem 

 ponderum. Idem fiat experimentum in profundis minerarum 

 alte sub terra depressarum, utrum horologium hujusmodi non 

 moveatur velocius quam solebat, propter auctam virtutem pon- 

 derum. Quod si inveniatur virtus ponderum minui in sublimi, 

 aggravari in subterraneis, recipiatur pro causa ponderis at- 

 tractio a massa corporea terras. 1 



Similiter, sit natura inquisita Verticitas Acus Ferreae, tactae 

 magnete. Circa hanc naturam tale erit bivium. Necesse est 

 ut tactus magnetis vel ex se indat ferro verticitatem ad septen- 

 triones et austrum ; vel ut excitet ferrum tantummodo et habi- 

 litet, motus autem ipse indatur ex praesentia terrae ; ut Gil- 

 bertus opinatur, et tanto conatu probare nititur. Itaque hue 

 spectant ea quae ille perspicaci industria conquisivit. Nimirum 

 quod clavus ferreus, qui diu duravit in situ versus septentriones 

 et austrum, colligat mora diutina verticitatem, absque tactu 

 magnetis ; ac si terra ipsa, quae ob distantiam debiliter opera- 

 tur (namque superficies aut extima incrustatio terrae virtutis 

 magneticae, ut ille vult, expers est), per moram tamen longam 

 magnetis tactum suppleret, et ferrum exciret, deinde excitum 

 conformaret et verteret. Rursus, quod ferrum ignitum et 

 candens, si in exstinctione sua exporrigatur inter septentriones 



1 Nothing can be more ingenious than the instantia crucis here proposed. A series 

 of observations were made by Dr. Whewell and Mr. Airy to determine the effect on 

 the time of vibration of a pendulum, produced by carrying it to the bottom of a mine ; 

 but, probably from the effect of local attractions, the results were scarcely as satisfactory 

 as might have been expected. In the autumn of 1854, Mr. Airy instituted similar 

 experiments in the Harton Colliery. They appear likely to afford more satisfactory 

 results than the older series made at Dolcoath. 



Voltaire cites the passage in the text in support of his remark that " le plus grand 

 service, peut-etre, que F. Bacon ait rendu a la philosophie a ete de deviner 1'attraction." 

 But in reality the notion of attraction in one form or other (e. g. the attraction of the 

 sea by the moon) sprang up in the infancy of physical speculation ; and it cannot be 

 affirmed that Bacon's ideas on the subject were as clear as those of his predecessor 

 William Gilbert. (See note on De Aug. ii. 13.) By an error similar to Voltaire's, 

 some of Dante's commentators have claimed for him the credit of being the first to 

 indicate the true cause of the tides. The passage on which this claim is founded is in 

 the Paradise, xvi. 82. 



