DOUBLE-CURRENT MAGNETO-FARADIC APPARATUS. 281 



four intermissions of the rheotome, for each revolution of the soft 

 iron, produce four inductions of equal force ; 3, that the currents 

 which arise from these different inductions proceed alternately in 

 contrary directions. 



If, then, we faradize with two intermissions for each revolution 

 of the armature, we should obtain two powerful actions, and the 

 current will travel each time in the same direction. The two other 

 actioiiS, during which the current passes in a contrary direction, 

 are so feeble, that in man they give rise to no appreciable pheno- 

 mena, unless directed upon the retina, when tliey produce a phos- 

 phene. Hence, by the aid of its regulator, the spring of the 

 rheotome must be so placed as to give two intermissions, when 

 it is desired that the currents should pass always in the same 

 direction. 



We may therefore apply my magneto-faradic apparatus, the in- 

 termissions of which occur but twice for each revolution of the 

 armature, to the study of the influence exerted by the direction 

 of the currents upon the contractility or the sensibility.' The 

 same study cannot be pursued with four intermissions to each 

 revolution of the armature ; because the four inductions act with 

 equal force, and alternately in opposite directions. 



The four intermissions per revolution produce a current of 

 double rapidity. Their employment therefore fulfils numerous 

 indications ; as when we wish to act specially upon the sensibility, 

 or to study the muscular functions by the aid of faradization. But 

 although, with four intermissions, the current is twice as rapid as 

 in the instrument of Clarke, which gives only two intermissions per 

 revolution, its rapidity is still iusuflicieut for the study of the 

 muscular functions of the face. The same condition of the rheo- 

 tome renders the action of the magneto-electric instruments upon 

 the cutaneous sensibility much less powerful than that of the volta- 

 electric instruments, the intermissions of which may be made by 

 the trembler with a rapidity that is incalculable. 



C. — The Regulator oftlie Intermissions. 



No magneto-faradic apparatus is applicable to all the require- 

 ments of therapeutics, unless it possesses a mechanism by which to 

 obtain one, two, or four faradic excitations in the half-second ; 

 instead of very numerous intermissions during the same period of 

 time. I have contrived such an arrangement for my magneto- 



• It is well known that the electro- j have been used by Matteucci as the 

 physiological phenomena produced accord- basis of therapeutic deduction appli- 

 ing to the direction of currents traversing cable to man. 

 longitudinally the nerve-trunks of animals, 



