There never was a less sure man than Leeuwenhoek. He looked at this bee’s sting or that louse’s leg again and again and again. He left his specimens sticking on the point of his strange microscope for months--in order to look at other things he made more microscopes till he had hundreds of them!--then he came back to those first specimens to correct his first mistakes. He never set down a word about anything he peeped at, he never made a drawing until hundreds of peeps showed him that, under given conditions, he would always see exactly the same thing. And then he was not sure! He said: “People who look for the first time through a microscope say now I see this and then I see that--and even a skilled observer can be fooled. On these observations I have spent more time than many will believe, but I have done them with joy, and I have taken no notice of those who have said why take so much trouble and what good is it?--but I do not write for such people but only for the philosophical!” He worked for twenty years that way, without an audience. But at this time, in the middle of the seventeenth century, great things were astir in the world. Here and there in France and England and Italy rare men were thumbing their noses at almost everything that passed for knowledge. “We will no longer take Aristotle’s say-so, nor the Pope’s say-so,” said these rebels. “We will trust only the perpetually repeated observations of our own eyes and the careful weighings of our scales; we will listen to the answers experiments give us and no other answers!” So in England a few of these revolutionists started a society called The Invisible College, it had to be invisible because that man Cromwell might have hung them for plotters and heretics if he had heard of the strange questions they were trying to settle. What experiments those solemn searchers made! Put a spider in a circle made of the powder of a unicorn’s horn and that spider can’t crawl out--so said the wisdom of that day. But these Invisible Collegians? One of them brought what was supposed to be powdered unicorn’s horn and another came carrying a little spider in a bottle. The college crowded around under the light of high candles. Silence, then the hushed experiment, and here is their report of it: “A circle was made with the powder of unicorn’s horn and a spider set in the middle of it, but it immediately ran out.”