Mr Christie on the Magnetism of Iron in Rotation. 11 



This experiment may be equally well performed with closed 

 glass rods, as, according to Chladni's method, when tuned by 

 water poured in ; but the wide-bellied phials are most conve- 

 nient. Moreover, it is easily seen, that, in this manner, the po- 

 sition of the vanishing tone corresponds correctly enough with 

 the established position of the pitchpipe, and the angle of po- 

 larisation (if we may so express it) of the sound may be mea- 

 sured with exactness. 



Perhaps the experiment corresponds with this, that a pitch- 

 pipe quickly turned upon the axis of its handle ceases to give 

 out its tone to the air, which again appears when the turning 

 is suddenly stopped. 



Art. III. — On the History of the Experiments on the Mag- 

 netism exhibited by Iron in Rotation. By Samuel Hun- 

 ter Christie, Esq. M. A. of Trinity College, Cambridge, 

 Fellow of the Cambridge Philosophical Society ; of the 

 Royal Military Academy. In a Letter to the Euitor. 



Dear Sir, 



As the article in the last number of your valuable Journal, 

 giving an account of some of Mr Barlow's and my experiments 

 " on the magnetism of iron as exhibited by rotation," contains 

 statements which tend to convey very erroneous ideas respect- 

 ing the discovery of the influence which the rotation of iron 

 has on its magnetism, I feel that I cannot avoid making some 

 remarks on that article, although it is with great repugnance 

 that I notice circumstances connected with the subject. 



That there is a considerable inequality in the magnetism of 

 different parts of a piece of sheet-iron, every one must have 

 observed on bringing it near to a magnetised needle, and the me- 

 thod adopted by Mr Barlow of combining two plates, so that 

 the " opposite qualities' 1 should come in contact, is that which 

 immediately suggests itself for counteracting this inequality of 

 action ; but I am at a loss to see any connection between Mr 

 Barlow's having so combined two plates, and the experiments 

 in which I was engaged when I first discovered that the mag- 

 netism of iron is affected by rotation. I am not aware of Mr 



