With very powerful batteries, it has been possible to go further, and produce a light not much inferior to that of the sun. Messieurs Fizeau and Foucault, by comparing the light of a voltaic arc, produced by the action of three series of Bunsen's coils, of forty-six couples each, with the light of the sun in a clear sky in April, have established that the light-giving power of the sun is not more than twice and a half that of the electric light. The preceding numbers represent the light-giving power of the sun upon our globe, taking into account atmospheric absorption. Arago, on endeavouring to determine the intrinsic light-giving power of the sun, found that the intensity of the solar light is 52,000 times greater than that of a candle placed at one metre. But, according to more recent researches for which we are indebted to Mr. Edmond Becquerel, the result obtained by Arago is greatly inferior to the truth, and the light of the central star is 180,000 times greater than that of a candle placed at one metre. All the planets, attended by their satellites, and all the comets which accidentally manifest themselves to us, turn round the sun. The sun remains motionless in the midst of this imposing procession of stars, which circulate around him, like so many courtiers paying him homage. Thus, the sun is the heart of our planetary system; everything is drawn, everything converges towards him. Half-informed persons will exclaim, "What can be more simple! The sun being six hundred times the size of all the other stars put together, the phenomenon of the condition of all those stars around the sun is explained by the law of attraction, which prescribes that bodies shall attract in proportion to their mass. If the sun attracts the stars of our world to itself, it is because his mass is greater than that of all the other stars collectively." But such an answer would be erroneous, involving the common error of taking a word for a thing, an hypothesis for an explanation, of putting a term of language in the place of a logical consideration. When Newton conceived the hypothesis (and the phrase) of _reciprocal attraction of matter_, he was careful to state that he only proposed to characterise by a name a phenomenon which in itself is entirely inexplicable, and of which we know nothing but the exterior mode of its manifestation, that is to say, the mathematical law. We know that bodies go towards each other in the ratio of their masses, and in the inverse ratio of the square of their distances; but why do they go towards each other? This is what we do not know, and what we probably never shall know. If, for the word _attraction_ we were to substitute the word _electrization_, or, as Keppler did, the words _affection_, _sympathy_, _obedience_, &c., we should have a new hypothesis, with a new name, but the mathematical law would remain the same, the hypothesis only would be changed. The real cause which makes