398 ON MAGNETS. 



towards a maximum when the magnetising force increases without 

 limit. If the values of this force be taken as abscissae, and the 

 values of the magnetisation as ordinates, we obtain a curve like 

 OBL (Fig. 90), having an asymptote parallel to the axis of the 

 abscissa, and with a point of inflexion near the origin. 



Professor Rowland represents the phenomena in a different way. 

 Taking the values of induction F 1? as given directly by experiment, 

 as abscissae, and the values of yu as ordinates, he finds that his 

 experiments are represented very closely by the formula 



(9) 



in which #, , c, and d are constants depending on the nature 

 and quality of the metal. 



The curve represented by this equation has the general form 

 of a parabola with a diameter conjugate with the axis of the 

 abscissae ; it cuts this axis in two points, and the inclination of 

 the diameter depends on the constant b. The position of the 

 points of intersection with the axis depends on the values of- c and 

 d. The constant a evidently represents the maximum value of /*. 

 Professor Rowland's experiments give for this maximum at the 

 ordinary temperatures numbers between 3000 and 5000 in the 

 case of iron, and 300 in that of nickel. The curve assumes 

 another form when the temperature changes, and the deformation 

 appears to be far greater for nickel than for iron. 



425. HYPOTHESIS ON THE CONSTITUTION OF MAGNETS. 

 According to Poisson's theory the magnetisation of a medium is 

 produced by the separation of the magnetic fluids in the interior 

 of each particle, and as no limit can be assigned to the quantity of 

 neutral fluid which can exist in a definite volume, the magnetisation 

 itself might increase without a limit. 



We shall afterwards see how Ampere, starting from the magnetic 

 properties of electrical currents, was led to assume that each particle 

 of a magnetic substance is surrounded in the natural state by an 

 infinitely small electrical current, and constitutes an elementary 

 magnet. In a magnetic body withdrawn from all external force, 

 these elementary magnets are only subjected to their mutual actions, 

 and are turned indifferently in all directions. If the body is sub- 

 mitted to the action of a magnetic field the axes of the different 

 magnetised particles tend to take the direction of the field at each 



