Intelligence and Miscellaneous Articles. 233 



magnetic portions of the magnet and armature ; 3, the actions at 

 distance of the free portions of the magnet upon those of the 

 armature. 



The calculation can be accomplished if the distribution of the 

 magnetism in the magnet and armature is known. This, however, 

 can only be ascertained in few cases. Two such are treated in the 

 present memoir : in the first the magnet and armature constitute 

 by their combination a ring magnet ; in the second, a uniformly 

 magnetized sphere. 



In the first case no free magnetic portions occur, the carrying- 

 power is determined by the attraction of the masses present at the 

 contact-surfaces alone. With this case is connected the solution 

 of three problems. 



The first problem has respect to the determination of the maxi- 

 mum of carrying-power which can be imparted to a ring magnet. 

 This can be calculated from the greatest value the magnetic 

 moment of the unit volume of iron is capable of taking, and 

 amounts to 12450 grams for each square centimetre of contact- 

 surface. 



The second problem refers to the representation of the connexion 

 between the carrying-power and the intensity of the current by 

 which the ring is magnetized. This connexion cannot at present 

 be expressed by a valid formula ; but probably the nature of it 

 can be ascertained with tolerable accuracy. The carrying-power 

 rises at first in a much greater proportion than the intensity of 

 the current, until it attains a fourth part of its maximal value ; 

 thenceforward the carrying-power rises more slowly than the 

 current-intensity. In the vicinity of the value above given the 

 carrying-power remains during a considerable interval nearly pro- 

 portional to the intensity of the current. 



The third problem concerns the determination of the dependence 

 of the carrying-power on the situation of the plane which divides 

 the ring into magnet and armature. When these latter form un- 

 equal segments of the ring, the carrying-power is less, notwith- 

 standing the greater surface of contact ; it diminishes in nearly 

 the same proportion as the surface of contact increases when the 

 plane of contact moves away from the axis of the ring. 



If the magnet and armature form a spherical magnet, all three 

 sorts of forces come in to be calculated. The influence of the 

 free magnetic masses which are upon the surface of the sphere 

 diminishes the carrying-power. The relative carrying-power (i. e. 

 that which falls to the unit of surface of contact) is greatest when 

 magnet and armature are hemispheres ; but even in this case it is 

 only half as great as that of a ring magnet. The further the 

 plane dividing the sphere into magnet and armature is from the 

 centre, the less is the relative carrying-power ; so that the total 

 capacity of carrying diminishes with the- fourth power of the 

 radius of the surface of contact. — Siizung der matliematiscli-natur- 

 wissenschaftlichen Classe der Jcaiserl. Ahad. d. Wissensch. in Wien 

 vom 15. J'dnner 1880, pp. 14, 15. 



