The alchemists experimented on various substances, treated them by fire, then by water, then united them, and carefully noted the results. Thus far they were in the true path of science; but they could make little advance beyond this, because they began their work with some false notions which they could never lay aside. They believed, for instance, that earth, air, fire, and water were peopled by demons; and when the facts did not agree with their theories, they explained matters by saying that the demons were interfering. Of course they believed in the influence of the stars, and often they tried to connect the stars and the earth by odors. If a man wished to secure the influence of the sun, for instance, he mixed saffron, amber, musk, clove, incense, the brain of an eagle, and the blood of a cock, and burned them.

The alchemists had three aims in particular. One was to discover a "universal solvent," that is, some substance that would dissolve everything into its elements. The second was to make an elixir that would enable a person to keep youth and life as long as he chose. Even the reasonable Roger Bacon thought this was quite possible; and after the discovery of America, people felt sure that somewhere in the wonderful new land the elixir would be found. Many believed that the marvelous draught would not be compounded by an alchemist, but was only the water of some magic fountain. When Ponce de Leon made his voyage to America in 1512, he set out in eager hope of finding this fountain of youth, for he was fast becoming an old man, and he longed to be young again.

The third quest of the alchemists was to discover what was known as the "philosopher's stone." They thought that all metals were made of sulphur and mercury, that in gold the sulphur and mercury were pure, while in the baser metals they were more or less corrupt. If the "stone" could be discovered, this corruption would be cured or driven away from any metal, and pure gold would remain. Generation after generation of alchemists labored in this quest. Many of them were honest and were trying their best to make discoveries that would be of value to mankind. Others sought only a method of making gold and so winning riches for themselves. Then, too, there were numerous rascals who had a smattering of the learning of the alchemists and went about persuading people that they could turn the baser metals into gold or silver, and getting money from them for sharing the secret of the method. Chaucer tells the story of one of these quacks who turned mercury into the purest of silver before the face and eyes of a trustful priest and obtained forty pounds from him for the recipe. The secret was that he brought with him a beechen coal in which a hole had been bored and filled with silver filings. It was easy to slip this coal in with the others in such a way that the wax which stopped up the hole would melt and let the silver fall into the crucible. The second trick of the deceiver was to stir the mercury in the crucible with a hollow rod in which was an ounce of silver filings kept in with wax in the same manner. After the priest had paid his forty pounds and the quack had disappeared, he tried his magical recipe; but in spite of all his efforts not a bit of silver could be found in the crucible.

The alchemists did not discover the philosopher's stone, but in their experiments they did gain some useful knowledge. Among other things they discovered soap, they learned how to separate silver from lead, and how to make porcelain. The Chinese knew of gunpowder many centuries earlier; but Roger Bacon is thought to have learned that with sulphur, saltpetre, and charcoal an explosion might be produced, and so to have discovered it anew. The ideas of some of the alchemists ran far out into the future. Bacon predicted that the time would come when boats would move without oars, and wagons without animals to draw them, when men would be able to fly through the air, and bridges without any supporting piers would span the widest rivers. He believed, too, that an elixir would be discovered that would enable people to live as long as they chose.

Several of Bacon's predictions have long ago come to pass; but they probably seemed to the good folk of his time far more absurd than many strange things that appeared to them a matter of course. All through the period people of education believed that the earth was a sphere; but they were ready to accept without question the wildest stories of what might be seen in the parts that were unknown to them. In Africa, it was said, great dragons were found from whose brains precious stones might be taken, and also beasts so venomous that whoever looked them in the face fell dead. It was believed that tribes lived in that country who had three or four eyes in their foreheads. Other tribes fed upon nothing but honeysuckles dried in smoke by the sun. Ireland was the special country of wonders. In one lake, so the story went, a rod of hazel would turn to ash and one of ash to hazel. Another lake had quite as amazing properties, for if a rod was made to stand upright in the water, the part in the earth became iron, that in the water was turned to stone, while that above the water was not changed. In Ireland, too, there was said to be a little island whose inhabitants could never die. When they were overcome with the weaknesses of age, they had to be carried elsewhere that they might find relief in death. In Finland, so people thought, certain men had the power to raise the wind. They tied knots in a cord, and if they desired a gentle breeze, they let out the cord to one knot. For a storm, they let out to four or five knots. Concerning India, people would believe the most fantastic imaginings. Its ruler was thought to be one Prester John, or priest John, who had governed the land for many centuries. Some of his subjects were said to be more than five cubits in height. Others had dogs' heads and barked like dogs. Near the source of the Ganges were men who had no mouths. Naturally, they neither ate nor drank; but they lived on the perfume of flowers.

Concerning animals and plants there was a sort of imaginative natural history which was stated in so authoritative a manner and with so many details that it must have needed a brave man to doubt its truth. "A griffin," says an old book, "is a flying thing. Its head and wings are like the eagle's; the rest of the body is like that of a lion." The "enchirius," whatever that may be, is described as a little fish half a foot long which clings to a stone when a storm is coming, that it may not be blown about. Its ability to cling must have been considerable, for it was said that if it caught a good hold of a ship, it could hold it perfectly quiet. Still more startling is the statement that when a whale becomes old, earth collects upon his body to such an extent that herbs and small bushes take root and grow. Cranes, it was said, seat themselves comfortably on the ground when they are weary; but they always leave watchers on guard. The watchers stand on one foot. In the other foot they hold a little stone, so that if they chance to go to sleep the stone will fall and arouse them. No serpent will come into the shade of an ash tree; and if the creature be encircled partly with ash leaves and partly with fire, he will flee through the fire rather than touch the leaves. The young ravens live on dew until they begin to show black feathers. Then the mother bird feeds them. Toads and serpents cannot bear the fragrance of the grapevine blossom, and when the vine is in bloom, they escape from the vineyard. These are some of the "facts" of natural history as believed in the Middle Ages. Folk were taught that there were satyrs with horns and the feet of goats, cyclops with one eye in the middle of their foreheads, and people with eyes in their shoulders and neither nose nor head. They believed that certain men had made pacts with Satan, and in consequence were obliged once a year to take the face of a dog, a wolf, a bull, or a pig, and that these monsters searched the woods to find children to devour. But of all the fancies that were once regarded as facts of natural history, that of the phœnix was dearest to the good people of the age. There was only one phœnix in the world at a time. It lived from three to five hundred years, then, when it began to be weary and feeble, it made a nest of sweet smelling woods. This was set afire by the rays of the sun; and when it was well ablaze the bird entered the flames and was burned to ashes. Three days later, a little worm was found in the ashes, which grew and put on feathers and became another phœnix to take the place of the first. Cassia, it was said, was found in the nest of the phœnix, and either fell to the ground of its own accord or was struck down by leaden arrows. For some reason, people were not so willing to accept this story of the cassia as other marvels, and some ventured to say boldly that the tale was invented to raise the price of the article. About the mandrake, however, they were ready to believe anything, no matter how impossible. The root of the mandrake is often forked, and has a rough resemblance to a human body. That was enough to serve as a foundation for a story that it was the offspring of some person who had been put to death for murder. It shrieked when it was pulled, said the story; and to pull it was at best a dangerous business. He who set about it must wait until the wind blew from a favorable quarter. He must make three circles about the plant with a sword; but he must not venture to dig until after the sun had gone down. If one obeyed these directions carefully, he might hope to escape harm.

Various methods of divination were resorted to in order to read the future or to learn whether an enterprise would be likely to succeed. One way was to hang a ring inside a pitcher by a thread and read the fates by the number of times that it struck the sides of the pitcher. Sometimes a fire was built of certain kinds of wood, and it was believed that the shape and movement of the flames and the smoke would reveal things that were about to be. One might fast and pray and then open a Bible. The verse upon which his eye first lighted would be significant. Sometimes instead of the Bible a copy of Virgil was taken. To discover hidden treasure, one must use the hand of a man who had been hanged. Whether the predictions of a sorcerer were eventually shown to be true or false, the people believed in sorcery just the same; for if his words proved false, they simply declared that he was not a true sorcerer, and that some man of greater powers would have succeeded. Indeed, so far as the sorcerer himself was concerned, it was not well to succeed too often; for all magic was supposed to be more or less connected with the Devil, and if the magician was too successful, whispers would go abroad among his enemies that so intimate a friend of Satan ought to be burned to death or at least to be imprisoned. It was believed that at stated times sorcerers and witches met together in some gloomy and unlawful place to boast of the tricks they had played and learn of one another and of Satan how they might still further deceive those who consulted them. This meeting was known as the "Witches' Sabbath."

One great obstacle in the way of real progress in science was the general belief in analogy. A magnet will draw steel; therefore it was concluded that it would draw pain from the body. The "universal solvent" which the philosophers were ever hoping to discover would separate every substance into its elements; therefore it was supposed that it would also dissolve disease and do away with it. Another difficulty was that the causes of the phenomena of nature and the relation of cause to effect were so little understood that with most people if one event happened after another, this was regarded as sufficient proof that it was caused by that other. No matter how absurd and useless a medicine might be, if a sick man recovered after taking a dose of it, no one questioned that the medicine had wrought the cure.

A third great weakness in the science of the times was that instead of studying nature and trying to explain what they saw, the philosophers set out with definite opinions on numerous points and tried to make nature and their own observations fit the theories. The alchemists, as has been said, set out with the belief that all metals were made of sulphur and mercury, and they could never understand why the metals would not act like sulphur and mercury. Another difficulty was that if any two things looked alike, the philosophers were certain that there was some relation between them; but to discover what it was they used their imagination rather than their observation. For instance, crystal looks like ice; therefore they decided that if ice could be kept for many years, it would turn into crystal. Pearls have a dewy appearance and are found in the shells of oysters. That was proof enough that pearls came from dew; and the philosophers decided that in the nights of early spring the oyster opened its shell to receive the drop of dew and changed it into a pearl. In a thunderstorm, the sky is often covered with heavy, swiftly changing clouds; therefore it was regarded as evident that thunder is the noise produced by breaking up the clouds. This same fashion of fancying a connection between any two things that resembled each other was also carried into medicine. The wood sorrel has a heart-shaped leaf; therefore it would cure any disease of the heart. Liverwort, or hepatica, has a three-lobed leaf, and the liver has three lobes; therefore hepatica was of course beneficial to the liver. Certain ferns have seeds so tiny that they can hardly be seen by the naked eye; therefore fern seed had the power of making one invisible.

Such were some of the beliefs and superstitions of the people of the Middle Ages; but the folly of these vain imaginings was realized by some. One man who wrote an encyclopædia of general knowledge exclaimed against trying to read the future by noting the flight of a flock of crows, and said that he did not think it lawful to believe that God had revealed his counsel to crows. It is no longer necessary, as was the case in the seventh century, for a worthy bishop to beg his clergy not to observe Thursday, the day of Thor or Jupiter, as a day of rest, not to fear that a sneeze proved the presence of evil spirits, and not to visit sorcerers or makers of talismans. Nevertheless, there are many good folk even now who trust to absurd treatments of disease, who believe in signs and omens, in lucky and unlucky days and numbers, in the misfortune portended by the breaking of a or by the howling of a dog under the window, and in a thousand other superstitions; and even to-day the plain common sense of the man who did not believe that God revealed his counsel to crows would often be most welcome.