248 DESCRIPTION OF A MAGNETIMETER, BEIMG A NEW 



was usually directed towards the north. Four bars were prin- 

 cipally made use of. No. 1., consisting of a piece of iron- 

 wire, softened by heating, a quarter of an inch in diameter, 

 and six and a half inches long. No. 2., another piece of wire, 

 of two-tenths of an inch diameter. No. 3., a cylindrical bar' 

 of hardened steel magnetised, of the same dimensions as No. ]. 

 And, No. 4. a similar piece of steel softened by heating to red- 

 ness. With these, and the instrument already described, a 

 cfreat number of experiments were made ; the results of which, 

 in the form of propositions, are annexed ; and as almost every 

 experiment was repeated a number of times, I can give the re- 

 sults with the utmost confidence. What is called the Magne- 

 tic Axis in the following propositions, is to be understood as 

 the position pointed out by the dipping needle ; the Magnetic 

 Meridian is a vertical plane in the line of the magnetic north 

 and south ; and the Magnetic Equator is an oblique plane, to 

 which the magnetic axis is perpendicular. 



PROPOSITIONS, ^c. 



1. Iron bars become magnetical by position, excepting when 

 placed in the plane of the magnetic equator ; the upper end, 

 as regards the position of the magnetic equator, becoming a 

 south pole, and the lower extremity a north pole. 



Experiment 1. — Bar No. 1. placed in the groove of the moveable 

 limb, with the compass [H] at the distance of li inches from its 

 extremity, and the instrument north and south, (as in Fig. 3.) 

 did not disturb the needle at the angle of 20° ; but raised to an 

 angle of 46°, it repelled the north end of the needle one point, 

 ril° 15'], and at an angle of 73° two points. The north end of 

 the plate being depressed 2.5° below the horizontal, tlie bar in- 

 stantly exhibited an attraction of one point. Though the bar 

 was then changed end for end, still the same results were obtained, 



Exp. 2. 



