of the light. Dr. Tyndall will help me in shewing you that a blast of wind will blow out that light—the electric light can, in fact, be blown out easier than a candle. We have the power of getting our light where we please. If I cause the electricity to pass between carbon and mercury, I get a most intense and beautiful light—most of it being given off from the portion of the mercury between the liquid and the solid pole. I can shew you that the light is sometimes produced by the vapour between the two poles better, if I take silver, than when I use mercury. Here is the carbon pole, there is the silver, and there is the beautiful green light, which comes from the intervening portions. Now, that light is more easily blown out than the common lamp, the slightest puff of wind being sufficient to extinguish it, as you will see if Dr. Tyndall breathes upon it.
You see, therefore, how we are able, by using this electric spark, to get, first of all, the light into a very small space. That oil-lamp has a burner 3¾ inches in diameter. Compare the size of the flame with the space occupied by
