180 LIFE AND SCIENTIFIC LABORS OF STEFANO MARIANINL 



of dynamic electrieity ; and the discovery tlien made by Marianini, wliicli 

 may in some measure be considered as the ex])erimental basis of tlie 

 theory of Ohm, is still a fundamental one, uameh', that the action of 

 simple electro-motive machines ou ma.Qnets, to use his own words, is di- 

 rectly proportional to their surface, and that in a circuit having- a resist- 

 an(;e quasi null in comparison with that of the battery, the current of 

 a pile of a single pair has the same intensity Avith that of any number 

 of pairs whatever. 



In the same chapter the author studies the phenomenon of metallic 

 diaphragms interposed in a liquid stratum to the passage of the current. 

 The catalogue which is given in the essay of conductors of the first class, 

 according to the decreasing order of t\\6\r relative electro-motive power, 

 is established with much exactness, and may even now be said closely 

 to approximate the truth. 



In speaking of the conductibility of liquids, a subject in regard to 

 which the physicists of our own day well know the difticulty of arriving 

 at exact measurements, Marianini proves for the first time, what has 

 never since been contradicted, that the conductibility of liquids increases 

 with the temperature ; that this augmentation is less in liquids endowed 

 with a great conductibility, and that a heated liquid preserves for a certain 

 time in growing cold a greater conductibility than it first had at a given 

 temperature. Here be finds by experiment that the resistance of a 

 liquid stratum increases w^ith the thickness of the stratum, and shows 

 by many researches the augmentation of the effects of a battery by 

 increasing the size of the plate of copper which incloses the zinc. There 

 are also contained in the chapter on the conductibility of liquids some 

 experiments, among which I will cite, as worthy of being varied and 

 extended, that of the conductibility communicated by certain salts and 

 organic compounds to a liquid such as alcohol, which is itself scarcely 

 a conductor. 



In 182(5 Marianini read before the Atheneum of Venice a memoir on 

 Hitter's battery, and on secondary polarity, in which by many well- 

 devised experiments he more conclusively ]>roved, what had been as- 

 serted by Volta, that the polarities of secondary batteries depended on 

 the alterations which the current of the pile produces in the surface of 

 the metallic disks of Ritter's column. In fact, after these disks have 

 been washed and wiped dry. the column remains as active as before. 



More recently ]\Iarianini undertook the study of electro-physiological 

 phenomena, and in the memoir presented to the Academy of Eoveredf 

 in 1827, and which was translated in the Annales dc physique ct de 

 chimie, t. XL, p. 225, the experiments are described on which is founded 

 the law, still known in Germany as the law of Marianini, that the elec- 

 tric current in traversing the nerves in the direction of their ramifica- 

 tion, or the direct current, as Isobili called it, excites a contraction when 

 it enters and a sensation when it ceases to pass; and that, on the con- 

 trary, when the current is inverse or traverses the nerves in the direction 

 contrary to their ramification, a contraction is produced at the instant 

 at which it ceases to pass, and a sensation at that when it begins to 

 traverse the nerves. In tliis memoir, Marianini distinguishes the con- 

 tractions produced by electricity into idiopathic contractions, which are 

 excited whatever be the direction in which the current traverses the 

 muscles, and sympathetic contractions depending on the direction in 

 which the current traverses the motor nerves. In a second memoir, in 

 which he treats specially of the voltaic alternations, he shows that these 

 depend on the diminution of excitability of the nerves, produced by tha 

 l^assage of the current in a certain direction. Among these experiments, 



