“It seems to me that this is easily accounted for. One, or at least a few burns, is generally sufficient to convince us that fire _always_ burns; and when we are burned we always find it out, for the pain is directly communicated to the nervous system. But there are many reasons why we do not all know the relations between the drowning man and the altitude of Mt. Everest. In the first place, the rise of the water in the ocean is so slight that no human eye can see it. No direct observation can ascertain it. Again, there are not many men drowned. Again, nobody is watching for the rise of the water. We can only know it by reasoning up to it from a general principle; and you know that reasoning, in your present intellectual stage, is, as a whole, not very agreeable to the minds of the masses who are only seeking to keep the fierce wolf of poverty away from their door. Those are some of the reasons. “There is a relation between the _size_ of Ireland and the length of the earth’s day. The centrifugal force at the equator increases as the day is shortened. If the day were half as long as now, the water would tend to accumulate at the equator by virtue of the increased centrifugal force. Ireland is situated not far from the North Pole, and with increased centrifugal force at the equator, the water would recede from its present shore, which would increase the size of Ireland. If the day were _lengthened_ to forty-eight hours, Ireland would be, perhaps, entirely submerged. “Let us take another example where the truth is still more obscure. There exists a relation between the size of a growing plum in the Selvas (the luxuriant forest of the Amazon) and the _direction_ of the earth’s rotation. The earth rotates from _west_ to east, causing the trade winds to blow _always_ from the _east_. The Selvas is situated in the zone of trade winds, which brings abundance of moisture from the Atlantic ocean, because no mountains intervene. But, if the earth rotated from east to west, would change the direction of the trade winds from east to west. And then the Andes mountains would not let the moisture, which the trade winds would bring from the Pacific, pass over them, which would make a large part of the Selvas a desert instead of being the most fertile land in the world. So the plum would be very small or no plum at all. “Let us take one more example. There exists a relation between the amount of red clover and the number of cats; but we do not all see this truth or relation. Let us see if we can trace it. Red clover is fertilized here only by the humble bee. Field mice destroy humble bees by eating their honey; and cats catch mice. To have much red clover, then, we must have many humble bees; to have many humble bees, we must have few field-mice; and to have few field-mice, we must have many cats.