June 2, 1881] 



NATURE 



105 



natural ; the hardy genera are never associated with the 

 more tropical Eocene floras, and the sub-tropical genera 

 did not range farther north than the present temperate 

 latitudes, nor extend into the later Miocenes. Hardy 

 species occupied these latitudes in the old temperate 

 Eocene times, retreated as the temperature increased, and 

 re-descended from the north as it again decreased, reach- 

 ing finally as far south as North Italy. The habits and 

 even the species of the genera have not materially altered 

 since the Tertiaries commenced, and they appear to furnish 

 comparatively safe data for physiological inquiries. The 

 most remarkable fact taught by them, a fact beyond all 

 question, is that types now distinctive of widely separated 

 botanical regions actually lived side by side together in 

 Western Europe in the Eocene age. 



As the true nature of the various Eocene and Miocene 

 floras becomes unfolded, thanks principally to the able 

 work of Saporta, the fluctuations in temperature that 

 Europe and America have e.xperienced will be measur- 

 able and their ebb and flow calculable, with some 

 approximation to certainty. The sensational extremes 

 implied by the over-positive determination of fragments 

 that no human being could determine with certainty, will 

 then, it is to be hoped, be once and for ever discredited. 



THE STORAGE OF ELECTRIC CURRENTS 

 PRACTICAL electricians seem to have made up their 

 •l minds that a system for the distribution of electricity 

 for the purposes of electric lighting or ol driving electric 

 motors will be incomplete unless it comprises a means of 

 storage of the currents to provide against the risk of any 

 temporary derangement or inconstancy in the generating 

 apparatus. An accumulator of currents would in fact 

 render the same service in an electrical system as do gaso- 

 meters in systems for distributing gas, or the hydraulic 

 accumulators in a system of hydraulic machinery. 



At the present time much attention is directed to such 

 accumulators, or, as they have been hitherto called, 

 secondary batteries. 



The principle of the secondary battery dates back to 

 the very early days of Voltaic electricity, when in 1801, 

 one year after \'olta's " pile" had made its appearance, 

 Gautherot, a French savant, observed that wires of 

 platinum or of silver which had served as electrodes for 

 the decomposition of water containing a little salt or sal 

 ammoniac acquired the property of giving a brief current 

 after being detached from the pile. This phenomenon, 

 familiar to every electrician under the name of " polarisa- 

 tion of the electrodes," was observed again by Ritter of 

 Jena, in 1803, with electrodes of gold wire; and the 

 observation immediately led him to devise a battery from 

 which these secondary currents could be readily obtained, 

 and which constituted the first of all secondary batteries. 

 He tried many different arrangements, using various 

 metals — platinum, silver, iron, &c., but with lead he ob- 

 tained no result. He attributed this secondary action to 

 a soaking or accumulating of the two opposite kinds of 

 electricity into the surfaces of the plates or into the 

 intervening liquid. The true explanation was given 

 by Volta and RIarianini, and later by Becquerel, when 

 they showed that the action arose from the deposits 

 of oxygen and hydrogen, or of acid and of base upon 

 the two electrodes, whose surfaces thus became chemi- 

 cally changed and capable of acting towards one another 

 like the zinc and copper plates of an ordinary battery. 

 Grove, in 1843, brought the matter to a decisive proof by 

 constructing his curious gas battery, in which the positive 

 and negative poles were both platinum plates, the one 

 surrounded by oxygen gas, the other by hydrogen. 

 Ritter's failure to obtain any effect from electrodes of 

 lead arose from his employment of solutions of chlorides 

 as the liquid, the chloride of lead which resulted on the 

 passing of the current being a non-conductor, which at 



once stopped the current. M. Gaston Plants, who, in 

 1859, took up the study of the subject, found, after experi- 

 menting with many metals, that electrodes of leaJ, when 

 immersed in dilute sulphuric acid, gave rise to very 

 marked polarisation-effects ; for after passing through 

 lead electrodes the current from two Bun sen's cells, the 



FigL 



This figure represents two sheets oF tcad, separated by two sheets of canvas 

 rolled lip togellier and placed in a glass jar containing water, two strips 

 of sheet-lead protruding through the closed t'p of the j.ar. 



secondary currents were extremely strong and of consider- 

 able duration. He therefore constructed large secondary 

 batteries, using for this 1 urpose two sheets of lead im- 

 mersed in dilute acid. In order to reduce the internal 

 resistance by bringing the opposed surfaces as nearly as 

 possible together the two sheets were of large size and 



were rolled together in a spiral form, being kept from 

 touching by the interposition of sheets of coarse canvas, 

 or in later forms by means of bands of india-rubber. The 

 general form of a single cell of Plante's secondary battery 

 is shown in Fig. i. Such cells weighed over twenty 

 pounds, and when properly prepared had an electromotive 



