352 Prof. A. M. Mayer on the Effects of Magnetization 



vided into parts each corresponding to 32W °f an i ncn « Con- 

 sequently each division of the micrometer passed over by the 

 index indicated an increment of the length of the bar amounting 



t0 TW528° faninCl1 - 



u The quantities of electricity passing through the coil were 

 measured by an accurate galvanometer of tangents, consisting 

 of a circle of thick copper wire 1 foot in diameter, and a needle 

 J an inch long furnished with a suitable index. 



" The quantities of magnetic polarity communicated to the 

 iron bar were measured by a finely suspended magnet 18 inches 

 long, placed at the distance of 1 foot from the centre of the coil. 

 This magnetic bar was furnished with scales precisely in the 

 manner of an ordinary balance; and the weight required to bring 

 it to ahorizontal position indicated the intensityof the magnetism 

 of the iron bar under examination. 



' ' After a few preliminary trials, a great advantage was found 

 to result from filling the tube with water. The effect of the 

 water was, as De la Itive had already remarked, to prevent the 

 sound. It also checked the oscillations of the index, and had 

 the important effect of preventing any considerable irregularities 

 in the temperature of the bar. 



" The first experiment which I shall record was made with a 

 bar consisting of two pieces of well-annealed rectangular iron 

 wire, each 1 yard long, \ of an inch broad, and about \ of an 

 inch thick. The pieces were fastened together so as to form a 

 bar of nearly J of an inch square. The coil was placed in con- 

 nexion with a single constant cell, the resistance being further 

 increased by the addition of a few feet of fine wire. The instant 

 that the circuit was closed, the index passed over one division of 

 the micrometer. The needle of the galvanometer was then ob- 

 served to stand at 7° 20', while the magnetic balance required 

 0*52 of a grain to bring it to an equilibrium. It had been 

 found by proper experiments that a current of 7° 20' passing 

 through the coil was itself capable of exerting a force of 0*03 of 

 a grain upon the balance ; consequently the magnetic intensity 

 of the bar was represented by 0'49 of a grain. On breaking the 

 circuit the index was observed to retire 0*3 of a division, leaving 

 a permanent elongation of 0*7, and a permanent polarity of 0*42 

 of a grain. More powerful currents were now passed through 

 the coil and the observations repeated as before, with the results 

 tabulated below : — 



