330 Intelligence and Miscellaneous Articles. 



Besides, we can shorten the primitive fragment by successive break- 

 ings, and thus fix as many points as we will of the right line repre- 

 sented by equation (2) : the quantity of magnetism will be obtained 

 with great exactness. 



The determination of d is much less precise, since for settling its 

 value we have only one observation, that which refers to the mother 

 needle, and moreover d is always very small. Still, by multiplying 

 observations and taking their means we arrive at satisfactory results. 



By means of this method I have studied the manner in which 

 the quantity of magnetism and the distance of the poles vary when 

 needles 0-553 millim. in diameter, tempered very hard, are magnet- 

 ized by being passed through one and the same spiral, and the in- 

 tensity of the current is varied. 



Quantities of magnetism. — The average results obtained are re- 

 presented in the following Table, the numbers in both columns 

 being expressed in arbitrary units. 



Intensity of the Quantity of 



current. magnetism. 



3 . . hardly perceptible. 



5 0-12 



7 0-51 



9 1-09 



12 2-11 



13-8 2-89 



15 3-35 



18 5-65 



23 11-96 



28 17-90 



36 23-00 



! 40 24-00 



50 25-90 



oo 28-90 



Several physicists, amongst others Stoletow * and Eowland f , 

 have recently applied themselves to the determination of what the 

 former calls the " magnetizing-function " of various sorts of iron or 



TT 



steel; it is the ratio ^,of the quantity of magnetism H developed 



X 



either temporarily or permanently in unit volume of the substance 

 taken under the form of a cylinder of infinitesimal transverse di- 

 mensions in proportion to its length, to the force F which produces 

 the magnetism by acting in the direction of the axis of the cylinder. 

 The clearest way of representing this function consists in con- 

 structing a curve the ordinates of which are the quantities H, and 

 its abscissae the forces F. At first concave towards the positive 

 ordinates, it afterwards presents a point of inflection and approaches 

 asymptotically towards a parallel to the axis of the abscissae. 

 The numbers contained in the preceding Table are proportional 



* Philosophical Magazine, January 1873. \ Ibid, August 1873. 



