S80 Mr Watt's Experiments with the Magnetic Needle. 



the south pole, and that affixed to the wood the north, it will im- 

 mediately spring up from the horizontal position, and the south 

 pole will point almost straight upwards, towards the zenith, and 

 the north, of course, towards the nadir or centre of the earth. 

 If, then, without altering the bars in any way, we merely re- 

 verse the poles by passing the poles of two magnets along them 

 in the opposite direction, the contrary effect is produced ; and 

 the farther extremity of the steel bar becoming the north pole, 

 points toward the centre of the earth, and that affixed to the 

 wood upwards causing the other end of the wooden beam to 

 stand upright. 



In making this experiment, it is necessary to attend to the spe- 

 cific lightness of the instrument. The pivots ought to be of 

 smooth steel, and they ought simply to rest on two pieces of 

 glass or polished wire, placed on the top of the supporters of the 

 bar ; and nothing ought to touch the extreme points of the pi- 

 vots, as it prevents, by friction, the perfect developement of the 

 magnet's atttactions. The wood and the steel must also form 

 one perfectly straight bar. 



I would remark that, as all our compass needles are made of 

 considerable weight, and suspended by the centre, what yi,e have 

 considered the dip of the needle is merely the tendency the 

 needle evinces to the upright position, the south pole rising, and 

 the north dipping, more or less according to circumstances ; but 

 its position and weight prevent it from assuming the perpendi- 

 cular pointing. 



In the memoir which I had the honour of reading last winter 

 before the Wernerian Society, I took the liberty of making the 

 following observations respecting magnetism. That from the 

 phenomena I had observed by means of the solar compass and 

 other experiments ; that the magnetic needles were much in- 

 fluenced by the light and heat of the sun ; that the south pole 

 seemed attracted to the sun, and other celestial bodies ; that 

 probably a current of the magnetic fluid was ever in motion over 

 the surface of the globe, as over every other globular magnet, 

 that the magnetic intensity seemed, therefore, more equal near 

 the equator, and that to determine the magnetic intensity by the 

 vibrations of the needle, appeared not a very satisfactory way of 

 ascertaining it ; from the eff*ect the contingent causes already 

 mentioned had on the needle. And I conceive that the obser- 



