This enormous external current must be accompanied by some effect within the fish _equivalent_ to a current, the direction of which is from the tail towards the head, and equal to the sum of _all these external_ forces. Whether the process of evolving or exciting the electricity within the fish includes the production of the internal current, which is not necessarily so quick and momentary as the external one, we cannot at present say; but at the time of the shock the animal does not apparently feel the electric sensation which he causes in those around him. The gymnotus can stun and kill fish which are in very various relations to its own body. The extent of surface which the fish that is about to be struck offers to the water conducting the electricity increases the effect of the shock, and the larger the fish, accordingly, the greater must be the shock to which it will be subjected. The Chemical History of a Candle "The Chemical History of a Candle" was the most famous course in the long and remarkable series of Christmas lectures, "adapted to a juvenile auditory," at the Royal Institution, and remains a rarely-approached model of what such lectures should be. They were illustrated by experiments and specimens, but did not depend upon these for coherence and interest. They were delivered in 1860-61, and have just been translated, though all but half-a-century old, into German. _I.--Candles and their Flames_ There is not a law under which any part of this universe is governed that does not come into play in the phenomena of the chemical history of a candle. There is no better door by which you can enter into the study of natural philosophy than by considering the physical phenomena of a candle. And now, my boys and girls, I must first tell you of what candles are made. Some are great curiosities. I have here some bits of timber, branches of trees particularly famous for their burning. And here you see a piece of that very curious substance taken out of some of the bogs in Ireland, called _candle-wood_--a hard, strong, excellent wood, evidently fitted for good work as a resister of force, and yet withal burning so well that, where it is found, they make splinters of it, and torches, since it burns like a candle, and gives a very good light indeed. And in this wood we have one of the most beautiful illustrations of the general nature of a candle that I can possibly give. The fuel provided, the means of bringing that fuel to the place of chemical action, the regular and gradual supply of air to that place of action--heat and light all produced by a little piece of wood of this kind, forming, in fact, a natural candle.