pretty images seen in a reversed telescope, discovered a means—ever since universally employed—of producing artificial signals which have precisely the same properties as though they stood in infinite distance; or when a Newton made of the spectrum, a thing that had been gaped at as a mere curiosity a thousand times before, the foundation of modern optics?
The sudden arrival at a truth from all sides—a thing so frequent in the history of the sciences, which often makes it hard to decide to whom the honor of new discoveries properly belongs—of itself shows that cultivated minds in general have grasped the idea. The human race might be compared to a traveler in unexplored countries. As the booty he brings home is rich in proportion to the extent of his own intellectual acquirements, which enable him to distinguish what is new from what is hackneyed, so mankind has need of schooling in order to understand what is of importance in the events occurring round about. In short, one must be impressible in order to be impressed.
Ever since the fourth century of our era, the Chinese have used the magnetic needle as a nautical instrument, and thus were enabled to extend their voyages as far as India and Eastern Africa. The Arabians brought us into relations with India in the eighth century, and the Crusaders with the Orient in the tenth, and yet the mariner's compass was not introduced into Europe till the twelfth century.
Does it not seem wellnigh incredible that we cannot trace the use of the free-hanging plummet, as a means of observation, farther back than the period when the Arabians were our teachers in astronomy; nay, that only in the fifteenth century it found general acceptance by the exertions of our renowned countryman Georg von Peuerbach?
When, at the beginning of the last century, Amontons worked with entire success an optical telegraph; and Franklin, fifty years later, robbed the clouds of their lightning; and when both of these men were dismissed even by a learned body like the Paris Academy with stale witticisms; if for thousands of years countless aërolites have been seen to fall to the earth without ever giving rise to an inquiry as to the nature of meteors—the reason is always to be found in the self-same indisposition to receive what is new, which caused mediæval Europe to pass by unnoticed the golden teachings of a Roger Bacon or of a Leonardo da Vinci. Both of these stood high above Francis Bacon as inductive philosophers; but he had for his contemporaries men who had been taught by Copernicus, Galileo, Kepler, and others, some of the mighty consequences of that principle which Francis Bacon had now simply to formulate in order to have it universally accepted. Here and there other eminent men had, long before Roger Bacon himself, hit on the right way of investigating Nature. This assertion, too, rests on unquestionable evidence, which, however, is perhaps not so familiar to you. The visibility of