4 6 



SCIENCE. 



It is easy to understand tnat, with this arrangement, as 

 the resistance of the arc becomes greater, the strength of 

 the electro-magnet through which the current passes de- 

 creases, whilst the other electro-magnet becomes more 

 powerful ; so that the arm no longer remains in its vertical 

 position, and by its inclination influences the mechanism 

 which brings the carbons closer together. The contrary 

 effect is of course produced when the inverse action occurs. 

 An arrangement which, like the one in question, maintains 

 constant the resistance of the arc evidently does not exert 

 any effect upon the general intensity of the current in the 

 circuit ; for the variations of this intensity, outside of the 

 lamp, exert always the same effect upon the two electro- 

 magnets which control the latter.* The experiment with 

 the Foucault lamp gave such good results that I decided to 

 undertake the construction of a new lamp as free as possi- 

 ble from the defects inherent to the Foucault regulator, 

 and to those based upon the same principle. 



Fig. 1. 



After some carefully made experiments with lamps hav- 

 ing automatic regulation, and others regulated by hand, I 

 ascertained that the latter would give a constant light with 

 a much less number of battery cells than was requisite 

 with the former. Thus with hand regulators I could ob- 

 tain satisfactory results with 24 or even 20 Bunsen ele- 

 ments, whilst with the Foucault and Serrin regulators it 

 was necessary to employ at least 40. The cause of this in 

 the first place is that, in these regulating lamps the move- 

 ments communicated to the carbons are always too sudden 

 (prompte) for comparatively weak currents, and, in the 

 second place, that these movements are constant instead 

 of being proportionate to the intensity of the current pass- 

 ing by the voltaic arc. From this I naturally came to the 

 conclusion that, in order to obtain a lamp suitable for 

 practical working, it was necessary to apply the following 

 three principles, which I consider as fundamental : 



1. To maintain constant the resistance of the voltaic arc 

 we should not employ a constant mechanical force such as 

 that of a spring, but a weak derivation from the main cur- 

 rent, parallel to the voltaic arc. 



2. To obtain by means of a special derivation from the 

 main current the movements augmenting or diminishing 

 the distance between the carbons, in order that the 

 rapidity of these movements may be proportionate to the 

 intensity of the current producing the voltaic arc. 



3. To make arrangements such that this rapidity of the 

 movements communicated to the carbons should, at certain 

 periods, bo proportionate to the variations in their dis- 

 tance ; that is to say to arrange the apparatus so that, in the 

 case where the carbons have to be moved towards each 

 other through an appreciable space, the movement commu- 

 nicated to them may be more rapid than when they have to 

 be moved through a very shoit distance. 



In 1871 I had constructed a lamp which fulfilled the two 

 first of these principles, and which was brought before the 

 Moscow Society of naturalists. In this system I employed 



*Tilil 1- Mjmcwh it obtcurc ; what is meant, perhaps, is that the sum of 

 the currents traversing the two magnets is, with the adjustments adopted, 



a constant value. — Bi 



as motor a small electro-magnetic machine of Froment, 

 worked by a derivation from the principal current passing 

 by the carbons ; and above this electro-motor, the axis of 

 which was vertical, were placed the two electro-magnets of 

 the differential system above referred to. An armature 

 common to both and suspended between their poles like a 

 pendulum, reacted upon a double system of gearing, the 

 axis of which, furnished with two angle-wheels of unequal 

 diameter, would present to the electro-motor one or the 

 other of these wheels according as one or the other of the 

 two electro-magnets was the more energetic. As the wheels 

 in question corresponded to two opposite points of the 

 driving wheel, the movements produced were in opposite 

 directions and could increase or diminish the distance be- 

 tween the carbons with a rapidity greater or less according 

 to the intensity of the current, since the working of the 

 motor was dependent upon this intensity. The drawing of 

 this lamp has been in the polytechnic museum of Moscow 

 since the commencement of the year 1873. 



At the end of 1873, M. Jablochkoff, who at that period 

 had a mechanical workshop at Moscow, being convinced of 

 the superiority of the systems of constructing lamps on the 

 derived current principle, made in his workshop a lamp on 

 this principle. I shall not refer to the experiments with 

 this lamp, which gave full satisfaction to several persons. 

 For my own part, I was but partially satisfied, on account 

 of its complication, and because it did not fulfil the third 

 of the fundamental principles I had laid down. 



In 1874, I arranged a new lamp, the design of which I 

 brought before the physical section of the Moscow Society 

 of Naturalists, and which is represented by Fig. 1. 



E E' are electro-magnets disposed like those on the other 

 systems and having poles, a b, spread out in circular form 

 as in the Gramme machine. K is a Gramme or Siemens 

 ring, the rotary motion of which causes the carbons to move 

 through the intermediary of a double-thread screw, A, and 

 two nuts, B C, which carry the carbons. Lastly, D is a 

 regulating screw, for the purpose of raising or lowering the 

 luminous focus. 



The current passes from the positive pole of the genera- 

 tor to the negative pole by three derivations, one of which 

 includes the arc and traverses the ring by means of the 

 contact-pieces m n ; whilst a second, also including the arc, 

 excites the electro-magnet E (or both electro-magnets in a 

 given direction) ; and a third which, without passing by the 

 arc, influences the high resistance magnet E' (or both mag- 

 nets in contrary directions), so that the action of this magnet 

 upon the ring shall be in a reverse direction to that of E. 



Fig. 2. 



In consequence of this arrangement the action of the 

 electro-magnets upon the rinjr K is almost nil when the arc 

 possesses its normal resistance ; but when the resistance of 

 the arc augments the action of the electro-magnet, E be- 

 comes weakened, allowing E' to preponderate, and the ring 

 K will rotate so as to bring the carbons into closer prox- 

 imity. The contrary effect will, of course, be produced if: 

 the resistance of the arc should diminish. 



