Researches on Electro-magnetism. 199 



netic meridian being, as is known, proportional to the intensity 

 of the stream ; thence the stream passed onward to a copper 

 helix, within which the core of soft iron was placed. The helix 

 stood at right angles to the magnetic meridian, and the mag- 

 netism of the bar within it was determined by its action on a 

 freely suspended needle (No. 2) placed 88 centimetres eastward 

 from the helix. A cm-rent which delivers 1 cubic centimetre of 

 oxygen and hydi'Ogen at 0° temp, and 760 millims. tension in 

 one minute, was assumed as unit. To reduce the results given 

 by the needle (No. 1) to this unit, the tangent of the angle must 

 be multiplied by 70. 



We shall now explain the signs used in the foregoing "table. 

 The letters v and g contained in column c designate two chstinct 

 helices; the former consisted of 372 windings, and the latter of 

 482 windings of copper wii'e. 



The column headed a contains the angles which the needle 

 (No. 1) made wath the magnetic meridian; the cohmm s con- 

 tains the produots of the tangents of these angles and the factor 

 70 ; the column p contains the magnetizing force, obtained by 

 multiplying the strength of the stream s by the number of wind- 

 ings in the helix; v! is the angle which the helix alone, when 

 the stream passes through it, causes the needle (No. 2) to make 

 with the magnetic meridian ; and u is the angle caused by the 

 united action of helix and core; tan u — tan u' will therefore be the 

 measm'e of the magnetism of the bar, and this is contained in 

 the column headed m ; the last column contains the quotient 

 obtained by dividing the magnetism of the bar by the force ne- 

 cessary to evoke the said magnetism. 



Were the law that the magnetism of the bar is proportional 



to the strength of the current valid, the quotient — ought to be 



constant ; a glance at the last colixmn will, however, show that 

 this is by no means the case with the bar No. 1. When 



7H 



a weak current is applied, — is greater than when a strong cur- 

 rent is applied; the magnetism of the bar does not advance 

 in the same ratio as the galvanic power, but in a much smaller 

 ratio, which is quite analogous to the results obtained by Dub. 

 The bar No. 4, however, which, as before stated, was 44 milUms. 

 thick, fulfills the law. It woidd appear from this, that a bar of 

 soft iron, as regards its capacity for magnetism, may be roughly 

 represented to the mind as a vessel of fixed dimensions capable 

 of containing a certain quantity of fluid and no more. 



M. Miiller expresses the relation between the magnetizing 

 force, the magnetism thereby excited, and the diameter of the 



