82 Prof. E. Bouty's Studies on Magnetism. 



nent, developed by a current of given intensity in a bar placed 

 in the axis of a spiral excited by the current. Several of these 

 physicists treat also, subsidiarily, the same question for steel. 

 As regards the accessory phenomena accompanying magnetiza- 

 tion, they are so numerous and varied that they constitute an 

 inexhaustible mine which still, notwithstanding numerous 

 labours, has scarcely been touched. We will cite only those 

 memoirs which have the closest connexion with the subject of 

 the present investigation. 



Quetelet* studied the magnetism produced in a bar of steel 

 by friction with a magnet. He established that the magnetism 

 increases, up to a certain limit, with the number of the frictions, 

 according to precise laws, to which we will return by-and-by. 

 Hermann t and ScholzJ, under the direction of Franken- 

 heim§, proved an analogous augmentation when a bar of steel 

 is brought near the pole (free or covered with paper) of an elec- 

 tromagnet, or when a steel bar is several times introduced into a 

 spiral traversed by a current. 



Coulomb ||, and afterwards Lamont^f, in their numerous 

 studies on all branches of magnetism, have enriehed the science 

 with observations on the influence of the temper of steel upon 

 its moment of saturation, and on the phenomena which accom- 

 pany the union or separation of superposed magnetized plates. 

 Villari**, and long previously Abriaff, made some experiments 

 on the brief duration of the phenomenon of magnetization. 



The temporary magnetization of steel, observed for the first 

 time by Musschenbroek and (Epinus, has beeu the subject of 

 interesting memoirs by PoggendorffJJ and Wiedemann §§. 



But the most complete investigation we possess on steel magnets 

 is found in the recent labours of M. Jamin || ||. These researches, 

 which it is not our duty to estimate here, open to physicists a 

 path in some sort quite new, and in which we should be happy 

 to have made one step. 



I. Methods of Measurement. 

 The determination of the magnetic moment of a magnet is 

 most frequently effected by one of the two methods indicated 



* Ann. de Ckim. et de Phys. Ser. 4. vol. liii. 



t De naturali magnetismo in Chalybem inducendo quanto momento sit 

 tempus. Vratisl., 1865. 



X Quanti sit momenti tempus in magnetismo inducendo, certa quadam 

 jluidi galvaniciintensitate adhibita. Vratisl., 1863. 



§ Pogg. Ann. vol. cxxiii. || Memoires de VAcademie, passim. 



% Magnetismus. ** Pogg. Ann. 1873. 



ft Annates de Chimie et de Physique, Ser. 3. vol. i. 



XX Pogg. Ann. vol. xlv. §§ Galvanismus, vol. ii. 



Illl Comptes Rendus de VAcad. des Sciences, 1873-74. 



