LARGE DOUBLE-CURRENT VOLTA-FARADIC APPARATUS. 257 



as is also proved by the experiments related above, and that it is 

 not a diminution of the magnetization of the core that puts a 

 check upon induction.^ 



These facts being completely established, I proceed next to their 

 application. I have no necessity to enter into the most recent 

 discoveries, in order to display the advantages of the application of 

 metallic tubes as graduators. It is enough to mention them, in 

 order to render intelligible their utility and importance in the 

 practice of localized faradization. The double graduation by the 

 double internal and external metallic cylinders is certainly prefer- 

 able to graduation by one alone, since the neutralization of the 

 currents is more complete when the tubes move together, and 

 when they cover the coils successively one can use at pleasure a 

 scale for graduation of double extent. 



D. — Moderator. 

 The graduator tube does not completely destroy the current 

 upon which it acts, so that the scale produced by graduation does 



9 Prior to the publication of 'the im- 

 portant work, Traite" de V e'lectricite theo- 

 rique et applique'e, in which M. de la 

 Hive has set forth the state of the science 

 with much learning and lucidity, I was not 

 aware thatHerr Dove, a physicist of great 

 merit, and professor of meteorology at 

 Berlin, had instituted, in 1842, researches 

 into the influence exerted by a copper 

 tube placed within a coil, and containing 

 a bundle of rods of soft iron. I believed, 

 when I laid before the Academy of 

 Medicine the investigations which form 

 the subject of this chapter, that I was the 

 first who had studied the influence of 

 metallic tubes upon the phenomena of in- 

 duction. I trust I may be forgiven for 

 my ignorance about this point in the 

 history of discovery in physics, when I 

 rei^eat that I am not a physicist. More- 

 over, the physicists who have witnessed 

 my labours, and whom I have consulted 

 upon the jDoint, have supported mo in my 

 belief. After having read in the treatise 

 of M. De la Eive an account of the re- 

 searches of Herr Dove upon the influence 

 of metallic masses introduced into a coil, 

 and having made myself acquainted with 

 the original work of Dove, I do not now 

 think it requisite to modify the terms in 

 which I described my own results in a 

 memoir addressed, in 1851, to the Aca- 

 demy of Medicine. 1. Indeed, Herr Dove 

 has not studied the influences exerted by 

 metallic tubes upon coils in the interior of 

 ■which there is no core. 2. If it be true 

 that this experimenter discovered that a 

 metallic tube, introduced into the axis of 



a coil, and containing a core of soft iron, 

 diminished the force of induction, it is 

 incontestable that he never said that the 

 influence of the tube increased in direct 

 ratio to its advance within the coil ; and, 

 if he had been aware of this, he would 

 doubtless have plainly stated it, on ac- 

 count of tiie practical importance of the fact. 



3. Herr Dove has not tried the etfect 

 of an external metallic tube, covering 

 the current of the secondary coil ; and, 

 in consequence, has not compared the 

 different action exerted by an inner and 

 an outer tube, either upon the currents or 

 ujion tlie magnetization of the iron core. 



4. Lastly, this celebrated physicist appears 

 not to have arrived at the same results 

 with myself, in the experiments which he 

 has made with magneto-faradic instru- 

 ments ; for, according to him, ice do not 

 see the intensify of the induced current 

 diminished by introducing a metallic 

 cylinder tvithin the induction coil, and 

 over the bundle of iron wires in its axis, 

 lohen ice magnetize these wires by the 

 approach of a magnet, instead of by a 

 voltaic current circidating in the coil. My 

 own experiments have convinced me that 

 metallic tubes neutralise the currents of 

 the primary and secondary c*ils of mag- 

 neto-faradic instruments, when they cover 

 their reels, just as completely as tliey do 

 the currents of volta-faradic instruments. 

 In the succeeding Part will be set forth a 

 demonstration of the facts, applied to the 

 graduation of ray magneto-faradic appar- 

 atus. 



