532 Prof. D. E. Hughes. [Mar. 17, 



It is not necessary to use a wire to produce these effects ; still more 

 powerful currents are generated in hars, ribbons, or sheets of iron ; 

 thus, no matter what external form the iron may .possess, it still 

 produces all the effects I have described. 



It requires a great many permanent twists in a wire to be able to 

 see any effect from these twists, but if we give to a wire, 1 millim. 

 diameter, forty whole turns (or until its fibres become separated) we 

 find some new effects ; we find a small current of 10° in the same 

 direction as its molar twist, and on giving a slight twist (20°) 

 the sonometric value of the sound obtained is 80°, instead of 50°, the 

 real value of a similar untwisted wire ; but the explanation will be 

 found by twisting the wire in a contrary direction to its molar twist. 

 We can now approach the zero but never produce a current in the 

 contrary direction, owing to the fact that by the spiral direction, due 

 to the fibrous molar turns, the neutral position of its molecules is no 

 longer parallel with its wire, but parallel with its molar twist, con- 

 sequently an elastic strain in the latter case can only bring the mole- 

 cules parallel with its wire, producing no current, and in the first 

 case the angle at which the reaction takes place is greater than before, 

 consequently the increased value of its current. 



The measurements of electric force mentioned in this paper are all 

 sonometric on an arbitrary scale. Their absolute value has not yet 

 been obtained, as we do not, at our present stage, require any except 

 comparative measures.* Thus, if each wire is of 1 millim. diameter 

 and 20 centims. long, all render the same stress in the axis of its coil. 

 I find that the following are the sonometric degrees of value : — 



c 



Soft iron 60 Tertiary current. 



Hard drum iron 50 „ 



Soft steel 45 „ „ 



Hard tempered steel 10 „ 



Copper, silver, &c —0 



Copper helix, 1 centim. diameter, 



20 turns in 20 centims 45 Secondary currents. 



Iron, spiral, ditto 45 „ „ 



Steel 45 „ „ 



The tertiary current increases with the diameter of the wire, in a 

 proportion which has not yet been determined ; thus, an ordinary hard 

 iron wire of 1 millim. diameter giving 50°, one of 2 millims. diameter 

 gave 100° ; and the maximum of force obtained by any degree of 

 torsion is at or near the limit of elasticity, since as soon as we pass 

 this point, producing a permanent twist, the current decreases, as 

 I have already shown in the case of a permanent twist. Thus, the 



* 50° sonometer has the same electromotive force as 0*10 of a Daniell battery. 



