how did it become what it is? by what steps of change, by what mode of force did the substance, the phenomenon, the organism, the habit or the event arise?]

The superiority of Man over other animals inhabiting this planet, of civilised over savage man, and of the more civilised over the less civilised, is proportioned to the extent which his thought can grasp of the past and of the future. His memory reaches farther back, his capability of prediction reaches farther forward in proportion as his knowledge increases. He has not only personal memory which brings to his mind at will the events of his individual life-he has history, the memory of the race; he has geology, the history of this planet; he has astronomy, the geology of other worlds. Whence does the conviction to which I have alluded, that each material form bears in itself the records of its past history, arise? Is it not from the belief in continuity? Does not the worn hollow in the rock record the action of the tide, its stratified layers the slow deposition by which it was formed, the organic remains imbedded in it, the beings living at the times these layers were deposited, so that from a fragment of stone we can get the history of a period myriads of years ago? From a fragment of bronze we may get the history of our race at a period antecedent to tradition. As science advances our power of reading such history improves and is extended. Saturn's ring may help us to a knowledge of how our solar system developed itself, for it as surely contains that history as the rock contains the record of its own formation.

By this patient investigation how much have we already. learned, which the most civilised of ancient human races ignored! While in ethics, in politics, in poetry, in sculpture, in painting, we have scarcely, if at all, advanced beyond the highest intellects of ancient Greece or Italy, how great are the steps we have made in physical science and its applications! But how much more may we not expect to know!

We, this evening assembled, Ephemera as we are, have learned by transmitted labour, to weigh, as in a balance, other worlds larger and heavier than our own, to know the length of their days and years, to measure their enormous distance from us and from each other, to detect and accurately ascertain

the influence they have on the movements of our world and on each other, and to discover the substances of which they are composed; may we not fairly hope that similar methods of research to those which have taught us so much may give our race farther information, until problems relating not only to remote worlds, but possibly to organic and sentient beings which may inhabit them-problems which it might now seem wildly visionary to enunciate-may be solved by progressive improvements in the modes of applying observation and experiment, induction and deduction?

231

ON A NEW VOLTAIC COMBINATION.

Phil. Mag., 1839.*

MR. PORRETT was, I believe, the first who employed a bladder to separate the liquids in the operating cell of the voltaic pile. M. Becquerel, by introducing this into the exciting cells, has shown us how to render constant the primitive intensity of the battery by preventing cross precipitation; Mr. Daniell has remedied some practical defects in M. Becquerel's arrangement, and his form of battery is undoubtedly the best of any that have been hitherto proposed.

In a letter published in the 'Philosophical Magazine' for February I endeavoured to show, that in addition to the immense benefit derived from constancy of action, which was the object aimed at by these gentlemen, the combination of four elements was capable of producing a much more powerful development of electricity than that of three, as by this means we have nearly the sum of chemical affinities instead of their difference; I also there suggested that if the principles I had laid down were true, there was every probability of superior combinations being discovered. I have lately been fortunate enough to hit upon a combination which I have no hesitation in pronouncing much more powerful than any previously known. The experiments which led to it are curious, and possess an interest of their own, as they prove a well-known chemical phenomenon to depend upon electricity, and thus tighten the link which binds these two sciences. The effect to which I allude is the dissolution of gold in nitro-muriatic acid; this metal, as is well known, not being attacked by either of the acids singly. The following experiments leave, I think, no doubt as to the rationale of this phenomenon :—

From the Comptes Rendus, Académie des Sciences, Paris,

I. Into the bottom of a wine glass I cemented the bowl of a tobacco-pipe; into this was poured pure nitric acid, while muriatic acid was poured into the wine glass to the same level; in this latter acid two strips of gold-leaf were allowed to remain for an hour, at the end of which time they remained as bright as when first immersed. A gold wire was now made to touch the nitric acid and the extremity of one of the strips of gold-leaf; this was instantly dissolved, while the other strip remained intact.

2. The experiment was inverted, but offered some difficulty, as the gold would not remain an equally long time in the nitric acid, from the effect of the nitrous gas; enough, however, was ascertained to prove that to the gold in this acid contact made little or no difference; while the gold in the muriatic was always dissolved.

3. A platina arc was used for connection instead of gold; the effect was the same.

4. The outside of the pipe was coated with gold-leaf, leaving scarcely any part exposed; a strip was placed in the muriatic acid as before, and when contact was made with the nitric acid this strip was destroyed, while the coating of gold directly across the line of junction was unhurt.

5. The nitric acid was stained with a little tournesol; when contact was made, I could not see that the muriatic acid acquired any of the colour.

6. Nitrate of copper was used instead of nitric acid; the effect was the same, but took place more slowly, and I could detect no precipitation on the negative metal.

7. I now made gold-leaf in muriatic acid the electrodes of a single pair of voltaic metals; the acid was decomposed and the positive electrode was dissolved.

From all this I think we may pronounce the action to be as follows as soon as the electric current is established, both the acids are decomposed, the hydrogen of the muriatic unites with the oxygen of the nitric, and the chlorine attacks the gold.

In all these cases the currents were examined with a galvanometer, and in all the gold which was dissolved represented the zinc of an ordinary voltaic combination. The greatest deflection was obtained with platina, gold, and two

acids. It now occurred to me that as gold, platina, and two acids gave so powerful an electric current, à fortiori, the same arrangement, with the substitution of zinc for gold, must form a combination more energetic than any yet known. I delayed not to submit this to experiment, and was gratified with the most complete success. A single pair, composed of a strip of amalgamated zinc an inch long and a quarter of an inch wide, a cylinder of platina three-quarters of an inch high, with a tobacco-pipe bowl and an egg-cup, readily decomposed water acidulated with sulphuric acid. In this battery the action is constant, and there is no precipitation on either metal. It offers the great advantage of being able to utilise the action of concentrated nitric acid. I tried the same arrangement, substituting for the muriatic acid caustic potass, which was suggested to me by a well-known experiment of M. Becquerel: the action was equally powerful; and I should prefer this arrangement, as there is no necessity for amalgamating the zinc, but for a fatal objection-the nitrate of potass, crystallising in the pores of the earthenware, splits it to pieces; except, therefore, a new description of diaphragm be discovered, which will bear the action of powerful acids, this combination must be abandoned.

I diluted the muriatic acid with twice its volume of water, and the effect was not perceptibly inferior. I then tried sulphuric with four or five times its volume of water; the intensity was a little diminished, but so little that I should prefer this combination to any other, as cheaper, exercising less local action on the zinc, and by no possibility endangering the platina. The nitric acid may be the common acid of commerce, but must be concentrated. If the hydrogen, instead of being absorbed by the oxygen of the nitric acid, is evolved on the surface of the platina, the energy of action is lowered and is no longer constant.

Great advantage will be found in employing a cell divided by a porous diaphragm for a decomposing cell; thus, if oxygen gas be wanted, the positive electrode should be put into dilute sulphuric acid and the negative into concentrated nitric. If chlorine be wanted, the positive into muriatic, the negative into nitric; if hydrogen, both into muriatic, the positive one