INSTRUMENT FOR MEASURING MAGNETIC ATTRACTIONS, &C. 249 



Exp. 2. — A bar of cast iron of the same magnitude was found to pos- 

 sess much less magnetism of position than the above. With the 

 compass 1\ inches from the end of the bar, No. 1., produced a 

 deflection of 11°, when elevated 29* above the plane of no-attrac- 

 tion : while the bar of cast iron, though of a soft kind, required to 

 be elevated 68° above the plane of no-attraction, before an equal 

 repulsion was produced. When the bar No. 1., was raised to the 

 angle of 68° above the plane of no-attraction, it repelled the com- 

 pass-needle 27*. 



Exp. 3. — Iron-bars of similar thickness, but of unequal lengths, were 

 found to possess different capacities for magnetism of position. 

 Thus a bar one-fourth of an inch in diameter, and nine inches 

 long, elevated 70*, caused a deflection in the compass-needle of 

 23* 45' ; the same reduced to 6j inches long, then repelled the 

 needle 18* ; and a portion of the same 2^ inches long, only repel- 

 led the needle f 30'. 



2. No attraction or repulsion appears between a magnetised 

 needle and iron-bars ; the latter being free from permanent 

 magnetism, whenever the iron is in the plane of the magnetic 

 equator ; consequently by measuring the angle of no-attrac- 

 tion, in a bar placed north and south, we discover the magne- 

 tic dip. 



Exp. — With one end of the bar No. 1. compass 2| inches distant, 

 the elevation of the plane of no attraction, at Liverpool, was 20°, 

 with the other end of the bar 17^°; the mean or co-dip 18-|° ; dip 

 71°i. On the coast of Greenland, in July last, Latitude 70° 36', 

 Longitude 17° 30' W. the mean angle of no attraction was 14°, 

 making the magnetic dip 76°. 



Remark. — For the purpose of making use of this instrument for 

 finding the dip, it is necessary to employ a very small needle, in 

 comparison of the bar of iron, and to place the needle as far distant 

 as it will conveniently act ; otherwise the magnetism infused into 



the 



