NOVUM ORGANUM. 153 



depth, in order to see whether the clock move more quickly 

 from the increased power of the weights.* But if this 

 power be found to diminish at a height, and to increase in 

 subterraneous places, the attraction of the corporeal mass 

 of the earth may be taken as the cause of weight. 



Again, let the required nature be the polarity of the steel 

 needle, when touched with the magnet. We have these 

 two ways with regard to this nature. Either the touch of 

 the magnet must communicate polarity to the steel towards 

 the north and south, or else it may only excite and prepare 

 it, whilst the actual motion is occasioned by the presence 

 of the earth, which Gilbert considers to be the case, and 

 endeavours to prove with so much labour. The particulars 

 he has inquired into with such ingenious zeal amount to 

 this: 1. An iron bolt placed for a long time towards the 

 north and south acquires polarity from this habit, without 

 the touch of the magnet ; as if the earth itself operating but 

 weakly from its distance (for the surface or outer crust 

 of the earth does not, in his opinion, possess the mag 

 netic power), yet, by long continued motion, could supply 

 the place of the magnet, excite the iron, and convert and 

 change it when excited. 2. Iron, at a red or white heat, 

 when quenched in a direction parallel to the north and 

 south, also acquires polarity without the touch of the 

 magnet ; as if the parts of iron being put in motion by ig 

 nition, and afterwards recovering themselves, were at the 

 moment of being quenched more susceptible and sensitive 

 of the power emanating from the earth, than at other times, 

 and therefore, as it were, excited. But these points, though 

 well observed, do not completely prove his assertion. 



An instance of the cross on this point might be as fol 

 lows. Let a small magnetic globe be taken, and its poles 

 marked, and placed towards the east and west, not towards 

 the north and south, and let it continue thus. Then let an 

 untouched needle be placed over it, and suffered to remain 

 so for six or seven days. Now the needle (for this is not 

 disputed), whilst it remains over the magnet, will leave the 

 poles of* the world, and turn to those of the magnet, and, 

 therefore, as long as it remains in the above position will 

 turn to the east and west. But if the needle, when removed 

 from the magnet, and placed upon a pivot, be found im 

 mediately to turn to the north and south, or even by degrees 



* The attractive power to the centre is on the whole diminished in mines, be 

 cause the earth above attracts in the contrary direction. 



