Jan. 30. 1879] 



NATURE 



295 



tube should be supported by an outer tube of equal length 

 and thickness, but composed of more tenacious metal — 

 wrought iron or gun metal. 



If this cannot be satisfactorily accomplished, then the 

 steel tube might be covered with at least two layers of 

 coiled tubes -breaking joint. In this case the tubes 

 should be screwed a.s well as shrunk over each other. If 

 the screwed part was slightly conical it would be possible 

 to adjust the tension with nicety. B. 



January 25 



THE ELECTRICITY OF THE TORPEDO 



'X* HE recent researches of Prof. Marey on the electric 



■*- discharge of the torpedo have been presented by 

 the author in an extended memoir published last year.' 

 We propose to present to our readers the main conclu- 

 sions reached by M. Marey, and the experimental de- 

 monstrations on which the principal of these are based. 

 But before entering into details of the experiments let us 

 indicate summarily the processes employed by M. Marey. 



In. previous researches,' made in 1871, he' had at his 

 disposal only the reactions of the muscles of the frog to 

 analyse the electric phenomena of the torpedo ; he caused 

 to be recorded, upon an inclosed plate, the shock of a 

 frog's muscle produced by the discharge of the electric 

 apparatus of the torpedo. The instant of the excitation 

 of an electric nerve or of the nervous centres of the 

 torpedo was recognised ; and it was seen that the move- 

 ment of the foot of the frog presented, at the instant of 

 excitation, a considerable retardation, equal, e.g., to four- 

 hundreds of a second, measured on the chronographic 

 scale. But into this total retardation entered several 

 diverse elements, which M. Marey took into account by 

 causing the muscle of the frog to contract by an excita- 

 tion directly acting upon it. The time lost by the muscle 

 of the frog representing nearly the half of the total re- 

 tardation, it was concluded that the time-test by the 

 electric apparatus is equal to that of the muscle of the 

 frog. 



Since these first researches, M. Marey has been able 

 to study more directly the electricity of the torpedo by 

 making use of the electro-magnetic signals of M. Deprez 

 and of Lipprnann's electrometer. 



M. Deprez' s signal is composed of a small electro- 

 magnet provided with an extremely light armature of 

 soft iron, which is applied to the coils when the current 

 which traverses them is closed, and which is drawn from 

 it, without delay in demagnetisation, at the moment of 

 the rupture of the current, by the contraction of the tight 

 mdia-rubber thread. The armature is provided with a 

 style which traces on the inclosed cylinder the closures 

 and ruptures of a current, the duration and frequency of 

 these successive acts, with such perfection that it is easy 

 thus to obtain the record of 1,000 vibrations per second. 

 In the tracing underneath the apparatus (Fig. i) is seen 

 the signals which it furnishes when acted on by a non- 

 continuous scale of 500 simple vibrations per second. 



It is this electro-magnetic signal which M. Marev placed 

 m the circuit formed by the torpedo, whose apparatus was 

 held between two metallic plates joined to the coils of 

 the apparatus by two conducting-wires. We shall see, 

 further on, what use he has been able to make of this. 



The second instrument by means of which certain 

 special points of the experiments have been made is 

 Lipprnann's capillary- electrometer. This apparatus is 

 formed essentially of a column of mercurv sustained by 

 capillarity, in a tube of extremely fine glass, the ex- 

 tremity of which is plunged in a bath of dilute acid. 

 VVhen the mercury of the apparatus and the acidulated 

 •water are placed in connection with two points of 



P.Vc.^r"'^^ ^*'*"" ^^^ Travaux du Laboratare de M. Marey." T. iii. 

 I'MTis: G. Masson. 1877. *• "'■ 



" Annales de I'tcole Nonnale Sup^rieure." 22 s., t. L, pp. 86-114. 



an electric circuit of unequal tensions the capillary 

 column is displaced and is carried towards the side of 

 strongest tension. This displacement is instantaneous, 

 and if the variations of electric tension are produced 

 successively with great rapidity we need not fear the 

 inertia of the capillary column. All the variations are 

 signalled whatever be their frequency. But as the move- 

 ments of the capillary column cannot be registered them- 

 selves, M. Marey has had recourse to photography in a 

 certain number of experiments. 



Let us now consider the results following the order 

 which we have indicated at the outset. 



I. A torpedds discharge is tiot a continuous current; it 

 is formed of a series of successive waves added one upon 

 another. 



The fundamental experiment upon which the demon- 

 stration of this proposition rests was performed with the 

 electro-magnetic signal (Naples, October, 1876). Having 

 compressed one part of the apparatus of an active tor- 

 pedo just drawn from the water between two metallic 

 plates furnished with conducting wires, M. Marey placed 

 the signal-machine of M Deprez in contact, and the 

 magnet being stimulated he heard a shrill noise resem- 

 bling that made by filing the end of a hard splinter of 

 wood. The vibrations of the armature, therefore, 

 had been produced by a series of successive electric 

 acts. In defining these vibrations one is justified in 

 stating that the discharge of the torpedo produced by the 

 animal as the result of a local excitation, was composed 

 of a variable number of waves or currents succeeding 

 each other. Fig. 2 represents two tracings so produced- 

 The great advantage resulting from the use of the elec tro- 

 magnetic signal was to show definitely that the discharge 

 is complex, an analysis which was not possible with the 

 frog's-foot signal. The muscle used as reagent does not 

 in fact react by means of the shocks apart from impulses 

 which are sudden and frequent ; it remains in a state of 

 permaneHt contraction. 



But the electro-magnetic signal, whilst showing the 

 dissociation of the torpedo discharge, furnished no other 

 result. It did not indicate how those successive waves 

 follow each other, it seemed even to lead to the con- 

 clusion that one wave is quite completed when the next 

 succeeds. At this point the induction is interrupted and 

 the experimentalist adopts another mode of solving this 

 question of the succession of waves in a discharge. M, 

 Marey, in fact, being convinced that the electric action 

 of the torpedo and muscular action should be assimilated, 

 and wishing to see in the discharge the analogue of 

 induced tetanus and even of voluntary contraction, could 

 not resign himself to the admission of an absolute dis- 

 continuity between the successive acts constituting a dis- 

 charge. Yet the electro-magnetic signal apparatus seemed 

 to pronounce his theory wrong. But on passing through 

 Lippmann's electrometer a slight current from the total 

 discharge, M. Marey observed that the column under- 

 went a series of successive impulses, the effects of which 

 unite together. This progression by successive jerks 

 indicated an increase of the intensity of the discharge, an 

 increase in which each new wave is joined to what re- 

 mains from those which have preceded it. Thus we de- 

 rive the proof that the electric waves are partially united 

 to one another like the muscular shocks of a tetanised 

 muscle. 



This first fact being gained, it was necessary to follow 

 up the analysis of the torpedo-discharge, determine the 

 nature of each of the independent electric acts which the 

 electro-magnetic signal had revealed, measure their dura- 

 tion, phases, &c. These different points have been eluci- 

 dated, each in its turn. 



2. To measure the duration of the electric-wave in the 

 torpedo, M. Marey has had recourse to the method 

 devised by Guillemin for determining that of very short 

 current, and used afterwards by Bernstein to measure the 



