May g, 1878] 



NATURE] 



45 



RHEOSTATIC MACHINE 



IT is known that Franklin made use of a series of 

 Leyden jars or fulminating plates, arranged in the 

 form of a cascade, to obtain strong discharges of static 

 electricity ; that, on the other hand, Volta, Ritter, Cruik- 

 shank, &c., were able to charge condensers by means of 

 the pile, and that these results gave rise to researches, 

 conducted both by calculation and experiment, on the 

 part of a great number of physicists. 



I have been led to study, in my turn, the static effects 

 of voltaic electricity,- by means of a secondary battery of 

 800 couples which I at present possess ; and I have de- 

 vised an apparatus which shows the intensity that these 

 effects may acquire. 



After having proved how easy it is with this battery to 

 charge rapidly an insulating plate condenser, sufficiently 

 thin, of glass, mica, guttapercha, &c., I combined a cer- 

 tain number of condensers, formed by preference of mica 

 covered with tinfoil, and arranged them as couples of 

 the secondary battery itself, so as to be easily charged in 

 quantity^ and discharged in {ension. 



All the pieces of the apparatus must be carefully insu- 

 lated. The commutator is formed of a long cylinder 

 of hard caoutchouc, provided with longitudinal metal- 

 lic bands, intended to unite the condensers at the surface ; 

 and traversed at the same time by copper wires, bent 

 at their extremities, for the purpose of uniting the con- 

 densers in tension. Small plates or metallic wires formed 

 into springs are placed in connection with the two arma- 

 tures of each condenser and fixed on an ebonite plate on 

 each side of the cylinder, to which a rotatory movement 

 can be given. 



If we put the two sides of the apparatus into commu- 

 nication with the secondary battery of 800 couples, even 

 several days after having charged it with two Bunsen 

 elements, and if we set the commutator in rotation, we 

 obtain, between the branches of the excitator, on which 

 the armatures of the extreme condensers abut, a series of 

 sparks entirely similar to those given by electric machines 

 provided with condensers. By employing an apparatus 

 of only thirty condensers, each of three square decimetres 

 of surface, I have obtained sparks four centimetres in 

 length. 



The tension of a secondary battery of 800 couples is 

 not necessary to produce marked effects with this appa- 

 ratus. By putting in action only 200 couples, we have 

 sparks of eight millimetres, and we may, without doubt, 

 by diminishing still more the thickness of the insulating 

 plates and multiplying the number of condensers, obtain 

 effects with a source of electricity of less tension. 



It is to be remarked that the discharges of static elec- 

 tricity, furnished by this apparatus, are not in directions 

 alternately positive and negative, but always in the same 

 direction, and that the loss of force resulting from the 

 transformation must be less than in the induction appa- 

 ratus ; for, as the voltaic circuit is not closed a single 

 instant on itself, there is no conversion of a part of the 

 current into heat. 



We may maintain the apparatus a long time in rotation 

 and produce a considerable number of discharges without 

 the secondary battery appearing sensibly weakened. This 

 is because each discharge employs only a very small quan- 

 tity of electricity, and because, as above stated, the circuit 

 of the battery is not closed by a conducting body. The 

 electricity of the source simply spreads over the polar 

 surfaces presented by all the condensers, in proportion 

 as they are discharged. This emission constantly re- 

 peated must nevertheless end by discharging a certain 

 quantity of electricity ; and when the instrument is charged 

 by a secondary battery, we must ultimately exhaust, 

 under the form of static effects, the limited quantity of 

 electricity which the current of the battery can furnish. 



Thus then, by another method than that of induction, 

 properly so-called, by means of a simple effect of static in- 

 fluence renewed without cessation, we effect the transfor- 

 mation of dynamic electricity, so that this apparatus may 

 be designated by the name of " rheostatic machine." 



Gaston Plant^ 



GEOGRAPHICAL NOTES 



The Berlin Geographical Society celebrated in charac- 

 teristic German fashion the fiftieth anniversary of its 

 foundation last week. Berlin, as our readers know, is 

 not the only German city possessing a geographical 

 society ; indeed it has two. In Hamburg and Bremen 

 are two excellent societies of this class, while the 

 Continent, generally, is overrun with them. Russia has 

 about a dozen, Belgium has at least two, Brussels and 

 Antwerp, Holland one if not more, France at least 

 half a dozen, Italy two or three, and the Scandi- 

 navian countries their own share. We do not consider it 

 a disadvantage that in maritime countries there should be 

 more than one geographical society, and we think it might 

 be beneficial if even in our own country associations 

 corresponding to the French societies of commercial 

 geography were established in our chief ports, Liverpool, 

 Glasgow, Bristol, Leith, Dundee. These might be branches 

 of or affiliated to the London society, and might catch 

 much that never reaches the latter. They might, 

 moreover, do considerable service in encouraging the 



