DIMENSIONS OP RINGS AND RODS OF IRON AND OTHER METALS. 211 



(e) The same current waa again sent through the coil, and the consequent deflection 

 was the same (or nearly so) as in (b). 



(/) The current was passed through the coil for the fourth time, and the resulting 

 deflection was about the same as in (c). 



The mean of the deflections found in (b) and (e) was taken as giving the true 

 elongation or retraction produced in a previously demagnetised ring or rod by a given 

 current The mean of (c) and (f) gave the changes which occurred when the iron had 

 been permanently magnetised by the same current. To these latter no great 

 importance is attached. 



The above series of operations was repeated with every different current that was 

 passed through the magnetising coil. 



Table I. gives the results of experiments made with the three iron rings and with 

 the rod No. 2. The magnetising forces are expressed in C.G.S. units and the 

 elongations as ten-rnillionths of the diameter of the rings und the length of the rod. 

 These results, except as regards ring No. (which are omitted to avoid confusion), 

 are plotted as curves in fig. 3, the abscissae representing the magnetising forces and 

 the ordinates the corresponding elongations. The curve of ring No. would, if plotted, 

 ascend very near to that of No. 2, and descend almost in a straight line with that of 

 No. 1, its apex being about midway between the two. 



TABLE I. IRON. 



Magnetising forces are expressed iu C.G.S. units; elongations in teu-niilliontliK of the diameter or 



length. 



2E2 



