April 2% 1875] 



NATURE 



519 



form of rods, which are cast on the flattened silver wires, as in a 

 battery described by De la Rue and Miiller,*, but in other 

 respects similar to the battery above' described ; the glass.'tubes 

 being, however, somewhat larger in diameter ; the rods of 

 chloride of silver are enclosed in tubes open at the top and 

 bottom, and formed of vegetable parchment, the object of these 

 vegetable parchment cases being to prevent contact between the 

 zinc and chloride-of-silver rods. The internal resistance of 

 batteries so constructed is only from 2 to 3 ohms per cell, 

 according to the distance of the zinc and chloride-of-silver rods, 

 and they evolve from 3 to 4'5 cub. centims. (o'lS to 0*27 cub. 

 inch) per minute, in a voltameter having a' resistance of II ohms. 

 Their action is remarkably constant. 



For the experiments detailed below, the vacuum-tubes were 

 generally used of about l^to 2 inches (j'Sto 5 centims.) in dia- 

 meter, and from 6 to 8 inches (15 '24 to 20-32 ceotims. ) long; also 

 prolate spheroidal vessels 6 inches by 3 inches (IS'24 by 7 '62 

 centims.) The terminals are of various forms, and from 4 inches 

 to 6 inches (I0'l6 to I5'24 centims.) apart, and made of 

 aluminium and occasionally of magnesium and of palladium ; the 

 latter showing some curious phenomena with a hydrogen residual 

 vacuum, which will be described in a future paper. A tube 

 which has given the most striking results is 8 inches (20'32 

 centims. ) long, and has a series of six aluminium rings varying in 

 diameter from f of an inch to about l\ uf an inch (o'95 to 3'I7 

 centims.), the thickness of the wire being about ,V (o'i6 



centim.) of an inch ; the rings are a little more than 1 inch (2 '54 

 centims.) apart ; and connecting wires of platinum pass through 

 the tube from each ring and permit of the length and other con- 

 ditions of the discharge being varied. 



At times the terminals of the battery were placed in connec- 

 tion with accumulators of different kinds — for instance, two 

 spheres of iSinches (4572 centims.) in diameter, presenting each 

 a superficies of 7-07 square feet (65 68 square decims.), and 

 cylinders of paper covered with tinfoil, each having a surface of 

 16 square feet (148 '64 square decims.) ; the globe and cylinders 

 were in all cases carefully insulated. Other accumulators were 

 composed of coils of two copper wires yV of an inch (o'i6 

 centim.) in diameter, covered with gutta percha, in two folds, 

 ■55 of an inch (o'o8 centim.) thick. One coil contains two wires, 

 A A' and B B', coiled side by side, each being 174 yards (159 

 metres) long, another with two wires each 350 yards (320 

 metres) long ; of the latter we have two coils. 



In addition to these accumulators we have several others 

 formed of alternate plates of tinfoil and insulating material, such 

 as paper saturated with paraiSn, and also sheets of vulcanite. 

 These are of various capacities and contain from 5 to several 

 hundred square feet. The largest has a capacity of 47'5 micro- 

 farads ; when it is discharged it gives a very bright short spark, 

 accompanied by a loud snap ; the charge deflagrates S inches 

 (20'32 centims.) of platinum wire, '005 inch (o"i27 millim. ) in 

 diameter, when it is caused to pass through it. Each accumu- 



FlG. 3. 



lator gives different results, but for the present we shall confine 

 ourselves to a description of the experiments made with the coil 

 accumulators. 



When the terminals of the battery are connected with the 

 wires of a vacuum-tube which permits of the passage of the 

 current, the wires (especially that connected with the zinc end) 

 become surrounded with a soft nebulous light, in which several 

 concentric layers of different degrees of brilliancy are seen In 

 most cases there is either no indication of stratification or only a 

 feeble ill-defined tendency to stratification ; the tubes selected 

 for these experiments were those in which the stratification did 

 not appear at all. 



When the battery, already in connection with the vacuum- 

 tube, was also joined, as in Fig. 2, on to one or more coil- 

 condensers (coupled to introduce a greater length of wire) in the 

 following manner, then immediately well-defined stratifications 

 appeared in the vacuum-tube. 



S Z represents the battery, V the vacuum-tube, C the coil- 

 condenser ; one terminal is connected with the end A of the 

 wire A A', and the other terminal with the end B of the second 

 wire B B' ; connections are also led to the wires of the vacuum- 



* * Journal of the Chem. Soc, Second Scries, vol. vi. p, 488 ; Comptcs 

 Keadus, 1868, p. 794. 



Fig. 4. 



tube. The ends A' and B' are left free ; and it is clear that the 

 coil forms a sort of Leyden jar when thus used ; an interval, 

 however short it may be, must elapse in accumulating a charge 

 which at intervals discharges itself and causes a greater flow in 

 the vacuum-tube in addition to that which passes continuously. 

 It may be stated that the capacity of the accumulator has to be 

 carefully adjusted to prevent any cessation of the current, to 

 avoid, in fact, a snapping discharge at distant intervals. The 

 periodic overflows, so to speak, which increase the current from 

 time to time, would seem to have a tendency to cause an inter- 

 ference of the current waves, and to produce nodes of greater 

 resistance in the medium, as evinced by the stratification which 

 btcomes apparent. To the eye no pulsation in the cun-ent is 

 apparent ; and in order to convince ourselves whether or not 

 there was really any fluctuation in the current when tl.e 

 apparatus was thus coupled up with the battery, we made 

 several experiments, and ultimately hit upon the following 

 arrangement : — 



The primary wire p p' of a small induction-coil, both with 

 and without the iron core, was introduced into the circuit as well 

 as the vacuum-tube V ; to the secondary wire, s s', of the induc- 

 tion-coil was connected a second vacuum-tube, V. Under 

 these circumstances there was no change In the appearance of 



