222 The Rev. Dr. Ritchie's Remarks on certain 



from the reaction of the armature : and the density also of the 

 armature has considerable influence over its inducing power, 

 both on the steel magnet and the electro-magnet ; if the arma- 

 ture applied to the electro-magnet be made of very hard steel, 

 it will not sustain so much weight from the same intensity of 

 galvanic current as if it be made of soft iron. 



Thus it will be obvious that the more the steel is allied to 

 iron in its tempei', the more closely the effect of the keeper 

 upon the steel magnet will resemble that upon the electro- 

 magnet. Hence the explanation of the action of the armature 

 upon the one will apply to the other. 



In order that no misconception of my meaning may take 

 place, I will give one application of the above reasoning to the 

 case of the electro-magnet. Suppose a feeble galvanic current 

 to have been passed around an electro-magnet, and that the 

 magnetism induced by this current is represented by a and b ; 

 then, according to the foregoing explanation, 2 a and 2 b will 

 represent the magnetism on each side of the centre of the ar- 

 mature ; and as this exceeds the magnetic power induced by 

 the voltaic helix in the electro-magnet by « 4- i, the armature 

 will induce a + 6 of magnetism in the electro-magnet. As 

 soft iron offers so little impediment to the inducing power of 

 the armature, this power may be considered to exert its maxi- 

 mum effect upon very soft iron, and its minimum on the 

 hardest steel : now suppose the electro-magnet to have received 

 an accession of magnetism from a stronger galvanic current, 

 which may be represented hy c + d, then the inducing power 

 of the armature will be raised to 2 (6 + d) at one extremity, 

 and 2 (a + c) at the other ; and the electro-magnet will have 

 now received from the armature c -{■ d more of magnetism, 

 and so on for all future additions of magnetism induced by the 

 voltaic helix, until the electro-magnet has attained the highest 

 state of magnetism it is capable of. 



XLVI. Remarks on certain proposed Improvements in the 

 Magneto-Electric Machine. By the Rev. William Ritchie, 

 LL.D., F.R.S., P7-qfessor of Natural Philosophy in the Royal 

 Institution of Great Britain and in the University of London. 



IN thelast Number of the Philosophical Magazine, p. 1 20, there 

 is a paper on Magneto-electric Machines, by Fred. MuUins, 

 Esq., M.P., of such an extraordinary nature, that I feel my- 

 self called upon to point out its fallacy and inconsistency. As 

 facts are by far the most stubborn things to get rid of, I shall 

 simply state two experiments, which will be quite sufficient, 

 without entering at all into the principles of the science. 



