72 Mr. Barnes on Magnetic Polarity. 



Res. It exhibited no signs of polarity. 



I anticipated the next conclusion, that the change of po- 

 larity would divide the difference between 45 degrees and the 

 commencement of the scale ; accordingly, 



Exp. 8. Giving the compass to Mr. Dodge and holding 

 the instrument to measure the angle, I raised the bar from 

 the east 22 \ degrees and said without looking at it " now the 

 needle is inverted." " True,' 1 said he, " so it is." 



The curious and interesting result then is, that a plane 

 elevated from the north, at an angle of twenty-two and a 

 half degrees, and cutting the horizon in a line due east and 

 west, is a neutral plane or magnetical equator, and that a 

 bar revolved on this plane shows no polarity, and if the bar 

 makes with this plane on the upper or south side any angle 

 equal to twenty two and a half degrees or greater, the low- 

 er end is the north pole ; and if the bar makes on the under 

 or north side of the plane, a less angle with the plane of the 

 horizon than the magnetical equator makes, the end which 

 touches the equatorial plane is the south pole. Whether 

 these results are uniform in various parts of the world, or 

 whether there are such lines as magnetical tropics, on each 

 side of the magnetical equator, as the above results seem to 

 to intimate, — whether the magnetical equator is the same in 

 different latitudes, or varies its position according to latitude, 

 future experiments must determine. 



Dr. Gilbert has mentioned the fact that opposite ends of 

 an iron bar equally affect the magnet, and in the same 

 way, and he accounts for the fact by supposing that the 

 earth magnetises the bar instantaneously. 



Is then the common remark, in the books, that a bar 

 becomes magnetic by long standing in a vertical position 

 strictly true ? And will not any such bar instantly change its 

 polarity by being inverted ? 



Should any of these facts or experiments appear to your- 

 self to be new or useful, they are at your service for publica- 

 tion in your valuable Journal. 



Yours most truly, 



D. H. Barnes. 



We learn from Mr. Barnes, that at the time of writing his 

 paper, he had not seen the remarks in our last number, 

 (page 232,) signed, A Surveyor. He considers them as a 

 covert and improper attempt to depreciate a valuable discov- 



