It is, indeed, as true now as in the time of Newton, that the great ocean of truth lies undiscovered before us. I often wish that some President of the Royal Society, or of the British Association, would take for the theme of his annual address "The things we do not know." Who can say on the verge of what discoveries we are perhaps even now standing! It is extraordinary how slight a margin may stand for years between Man and some important improvement. Take the case of the electric light, for instance. It had been known for years that if a carbon rod be placed in an exhausted glass receiver, and a current of electricity be passed through it the carbon glowed with an intense light, but on the other hand it became so hot that the glass burst. The light, therefore, was useless, because the lamp burst as soon as it was lighted. Edison hit on the idea that if you made the carbon filament fine enough, you would get rid of the heat and yet have abundance of light. Edison's right to his patent has been contested on this very ground. It has been said that the mere introduction of so small a difference as the replacement of a thin rod by a fine filament was so slight an item that it could not be patented. The improvements by Swan, Lane Fox, and others, though so important as a whole, have been made step by step. Or take again the discovery of anaesthetics. At the beginning of the century Sir Humphrey discovered laughing gas, as it was then called. He found that it produced complete insensibility to pain and yet did not injure health. A tooth was actually taken out under its influence, and of course without suffering. These facts were known to our chemists, they were explained to the students in our great hospitals, and yet for half a century the obvious application occurred to no one. Operations continued to be performed as before, patients suffered the same horrible tortures, and yet the beneficent element was in our hands, its divine properties were known, but it never occurred to any one to make use of it. I may give one more illustration. Printing is generally said to have been discovered in the fifteenth century; and so it was for all practical purposes. But in fact printing was known long before. The Romans used stamps; on the monuments of Assyrian kings the name of the reigning monarch may be found duly printed. What then is the difference? One little, but all-important step. The real inventor of printing was the man into whose mind flashed the fruitful idea of having separate stamps for each letter, instead of for separate words. How slight seems the difference, and yet for 3000 years the thought occurred to no one. Who can tell what other discoveries, as simple and yet as far-reaching, lie at this very moment under our very eyes! Archimedes said that if you would give him room to stand on, he would move the earth. One truth leads to another; each discovery renders possible another, and, what is more, a higher.