200 



TJie Variation of the Needle. 



mental facts by experiment; and the simplicity of the means employed 

 will, I trust, render them very evident, however novel the views ad- 



In the first place I will suspend an ordinary soft-iron nail, such as is 

 commonly used by carpenters, from this unmagnetic support, by a 

 thread. Tt is easily proved to have no magnetism and no polarity, but 

 when the bar of soft-iron, held in the plane of declination at the angle 

 of the magnetic dip is approached to this suspended nail a magnetic 

 action at once becomes apparent. The soft iron bar and the common 

 wrought iron nail each appear to have polarity and act precisely like 

 magnetic needles. This is solely the result of the position in which 

 they are placed. There is no magnet near them, neither is there any 

 electrical battery to affect them. They are simply under the influence 

 of the earth's own magnetism (or rather the pervading cosmical force) 

 which becomes apparent in them when these otherwise inert bits of 

 iron are placed in the exact position in which this force can act upon 



Thus we learn that what seems to be a single force, limited to pecu- 

 liarly treated bits of steel, is really only an evidence of an all-pervading 

 force; a force that is not only with us everywhere but which is travers- 

 ing or affecting every particle of matter, atmosphere and ocean, granite, 

 brick and mortar, the iron-rods of our machinery and the very nails 

 that secure the floors, all continuously vibrating under the influence 

 of this mysterious force which — in its widest earth-influence — we 



