70 



Intelligence and Miscellaneous Articles. 



netic properties of which it is susceptible under the influence of a 

 given current, or which, after the interruption of the current, harf 

 already lost all the magnetic properties which it is unable to retain 

 permanently ; so long as that state of equilibrium is not established, 

 neither torsion nor the reverse act otherwise than any other me- 

 chanical shocks. 



The experiment is made in the following manner : — A bar of soft 

 iron, well annealed, 1 metre in length and 15 millims. in diameter, 

 is fixed by one extremity, the other being placed in the centre of a 

 wheel, by means of which it may be twisted in two directions. It 

 carries two spirals, one of which is intended to receive the current 

 of a single element of Daniel's battery, while the other serves as a 

 spiral of induction : the latter is connected with a galvanometer. It 

 is unnecessary to state that the two spirals must be sufliciently far 

 apart that no direct induction can take place. When the current is 

 set up, the needle turns 90° towards the right, the north pole is fixed 

 and the south pole twisted ; when an inverse current is set up, the 

 south pole of the bar is fixed and the north pole twisted, and the 

 needle turns to the left. The following table will render the expe- 

 riments easily intelligible : — 



Remarks. 



1 The bar magnetized, any other me- 

 l chanical shock acts upon the needle 



J in the same direction as torsion. 



1 The bar being magnetized to the 

 I highest degree, the application of 

 j any force which does not produce 



J torsion leaves the needle at 0. 



I On reversing the current, the same 

 l phaenomena are presented in an in 

 verse direction. 



I The current was interrupted; the 



I bar became demagnetized at first 



to saturation. 



The coercive force of any kind of iron may be measured by the 

 number of torsions necessary to make it reach the point of saturation. 



Permanent Effects. — When a bar of iron or a bundle of iron wire 

 has been magnetized by means of a violent permanent torsion, under 

 the influence either of the terrestrial or any other current, it does 

 not behave like an ordinary magnet. When twisted or untwisted 

 temporarily in the direction of the permanent torsion, magnetization is 

 caused, or a direct current ; and twisting or untwisting in the contrary 

 direction causes demagnetization, or an inverse current. 



This experiment may be easily made with two bundles of the same 

 iron wire, which are suspended vertically, and twisted in such a way 

 as to make of one a right-handed helix and of the other a left-handed 

 one ; both have the north pole upwards and the south pole below. 

 On their introduction into the spiral, the needle turns towards the 

 right. But when, after having fastened the north pole of each 



