world which was held by the early Hebrews and which appears to us so fantastic, was, after all, based upon facts, but like many theories which have followed it, upon too small a body of fact to supply a firm foundation.

It has often been said that the theories so tenaciously held by one generation are abandoned by the next. To a large extent this has been true of the past, and the explanation is in part that scientists are not less fallible than others, but are subject to like limitations in prejudice, in undue reverence for authority, in regard for the science vogue of their time, and in many other conditions. To an even greater degree the overturning of scientific doctrines has been due to the failure of both the scientists and their critics to distinguish clearly between legitimate theory within those fields where views may be rigidly tested, and audacious conjectures which have been offered under the verisimilitude of facts to explain problems whose complete solution belongs to the remote future, if they may not be regarded as insoluble by any methods which have yet been discovered.

The process of eruption within a volcanic vent as regards its physical and chemical aspects offers a problem which, though by no means simple, may yet be subjected to observation and experimentation. and doubtless belongs to the realm of soluble scientific problems. The materials present at the earth's center and their peculiar state of aggregation, are by contrast very largely a subject of conjecture, and attempts to class these problems together lead to inexcusable confusion.

A theory has been defined as an explanation founded upon inferences drawn from principles which are established by evidence. By contrast the hypothesis is a supposition as yet untested. The working hypothesis of the scientist occupies an intermediate position and aims to explain, at

least in part and better than any other, a set of related phenomena which are already known, and it is considered to be in a probationary stage until confirmed through rigid tests the nature of which is suggested by the hypothesis itself. When so examined it may be found wanting; but, if well founded, experimentation is likely to result in its improvement by pruning of error quite as much as through enlargement of the body of truth which it contains.

The inheritance of knowledge by the ancients was, compared to ours, small indeed; and with their limited resources in materials and in methods of investigation, even more than we, they saw "through a glass darkly." It was therefore but natural that the theories which they evolved should have been largely the product of introspective reasoning. In consequence it was in the field of mathematics that they achieved their greatest triumphs, and as an inheritance a mathematical language was common to other fields of science even late in the seventeenth century. Viewing the marvels of the universe with their limited outfit of exact knowledge, the ancient philosophers invoked the supernatural and the mysterious to explain whatever was baffling and otherwise incomprehensible. Without books the dissemination of knowledge was limited to the narrowest channels and was accomplished by the disciples of each leader of thought, who was thus under the temptation of finding an answer to all questions and founding an individual school of philosophy.

With the invasions of the barbarian Huns and the Germanic tribes in the fifth century of the Christian era, there ensued the eclipse of civilization which we are accustomed to refer to as the "Dark Ages." Out of the darkness of these centuries of intellectual stagnation we catch a glimpse which indicates that individual minds were still active in their search for the truth.

It is the twentieth day of June in the year 1320. The bells of Verona are ringing in the bright Sabbath morning and the crowd is saluting with respect a tall and serious figure-the great Dantewho with slightly bowed head is entering the chapel of Santa Helena. Dante has to-day invited the whole educated world of Verona to assemble in this chapel and listen to his discourse entitled "De acqua et terra." He proposes to discuss the relative position of land and sea, and as he tells us himself, every one came at his bidding, "with the exception of a few, who feared by their presence to confirm the exceptional importance of others."'

With a gift for picture-writing never before equaled he has led his astounded contemporaries up to the abode of the saints and down into the depths of the lower world. Now to-day he is returning to the starting-point of his most powerful creation, to the critical examination of that which is greater than all the conceptions of poetry-the actual ordering of the universe.

Dante argued cogently for the spherical form of both the earth and the seas, and in accounting for the elevation of the land areas above the oceans, he even offered an early hint of the law of gravitation. The earth, he argued, can not elevate itself; nor can the cause be water, fire or air. He therefore suggested that the fixed stars might exercise this influence "after the manner of magnets.”

The new era which opened with the revival of learning after a thousand years of stagnation, was one dominated by new considerations within the realm of thought. The keynote of the period was the dominating influence of the Christian church, and for centuries all thinkers were required to make their expressions conform to the dogmas of the church of Rome. The emancipation supposed to have arrived with the Protestant Reformation was a partial one only, and complete freedom of thought was not secured until the modern period of science was ushered in in the latter half of the nineteenth century.

Living as we do when few obstacles are opposed to a full and free expression, it will

be profitable to review by means of examples the position of science in the sixteenth and seventeenth centuries. In declaring his belief in the heliocentric theory of the planets which Copernicus had promulgated, Galileo in 1597 wrote cautiously to the Polish astronomer:

It explains to me the cause of many phenomena which according to the generally accepted view are entirely incomprehensible. I have assembled many arguments for combatting the latter, but I do not dare to bring them into the light of publication. I would certainly risk it if there were more men like you.

With the telescope which he invented Galileo nightly studied the heavens from his little tower in the outskirts of Florence, and to his friend he unburdened his soul in unbounded admiration for the works of his Creator. He writes:

The prohibition of science would be contrary to the Bible, which in hundreds of places teaches us how the greatness and the glory of God shine forth marvelously in all His works, and is to be read above all in the open book of the heavens. And let no one believe that the reading of the most exalted thoughts which are inscribed upon these pages is to be accomplished through merely staring up at the radiance of the stars. There are such profound secrets and such lofty conceptions that the night labors and the researches of hundreds and yet hundreds of the keenest minds, in investigations extending over thousands of years would not penetrate them, and the delight of the searching and finding endures forever.

From this revelation of intellectual exaltation in one of the greatest apostles of science of all time, it is necessary to turn to a far different scene staged in one of the dark chambers of the Inquisition, if we would correctly interpret the spirit of his age. Bowed with years and racked by the cruel torture, Galileo is seen kneeling before the crucifix and repeating in broken sentences the dictation of his persecutors:

I bow my knee before the Honorable General Inquisitors, and touching the holy gospels I do promise that I believe and in future always will believe whatever the church holds and teaches for

the truth. I was commanded by the Holy Inquisition that I should neither believe nor teach the

false doctrine of the motion of the earth and the stationary attitude of the sun, because they are contrary to the Holy Scriptures. In spite of it I have written and caused to be printed a book in which I teach this cursed doctrine and have brought forth arguments in its favor. I have on this account been declared a heretic and worthy of contempt.

In order now to redeem myself in the eyes of every true Christian who with justice must hold me in contempt, I forswear and curse the errors and heresies referred to, and above all every other error and every opinion which is contrary to the teaching of the Church. Also I swear in future never either in spoken word or in writing to express anything on account of which any one could have me in like contempt, but I will, if I anywhere find or suspect heresy, reveal it at once to the Holy Tribunal.

It is not pleasant to dwell on the extreme conditions which determined the making of theories at this period and which continued for fully a hundred years beyond the time of Galileo. For advocating the Copernican doctrine Giordano Bruno was burned at the stake. More prudent, de Maillet left his theories of nature to be published only after his death and then with his name disguised as Telliamed through printing the letters in reverse order; while Scheuchzer avoided persecution by describing as a human victim of the Noachian deluge a gigantic fossil salamander, and thus became the butt of succeeding generations. Steno, "the wise Dane," through enjoying the favor of a powerful Christian prince, was more fortunate than most of his contemporaries, and has left us in his "Prodromus," one of the great scientific legacies of his age, now accessible to all through the excellent translation from the Latin by Professor Winter.

Inductive methods of reasoning came to play a larger part in the construction of theories as the control by both branches of the Christian church began to be relaxed. The feeling of relief from restraint brought,

however, a reaction in what was almost an epidemic of theories characterized by a carelessness of construction and an insecurity of foundation that were surpassed only by the ardor and the vindictiveness with which they were defended. The latter half of the eighteenth and the first part of the nineteenth centuries was thus a period characterized by notable controversies in science which affected the greater part of Europe. Theories were attacked or defended with almost fanatical bitterness, the aim of the advocates of each theory being apparently less to arrive at the truth than to win in the struggle. Geologists were divided into two hostile camps over the origin of basalt; the Neptunists led by the Freiberg school of Werner in Germany claiming that it was a chemical precipitate in the ocean, and the Vulcanists who followed James Hutton of Edinburgh, and believed the rock to be a product of the earth's internal heat. National boundaries were largely broken down and some of the most pertinacious and vindictive of the Wernerians were to be found in the British Isles.

On the other hand, the Neptunists had to meet in Germany a formidable champion of vulcanism in the poet Goethe, who, like Dante five centuries earlier, had a keen interest in science. For a time the bone of contention was found in a small hill near Eger in Bohemia, known as the Kammerbühl, a hill which Goethe stoutly maintained was "a pocket edition of a volcano.' He suggested a simple method by which the question might be settled, and proposed that a tunnel should be driven into the hill to its center. If the mountain was a volcano, as he believed, a plug of basalt should be found occupying its axis. A wealthy friend, Count Casper von Sternberg, undertook extensive excavations, which when completed in 1837 abundantly proved the correctness of the poet's position.

Another great controversy was waged

over the theory of the German geologist von Buch, known as the "Elevation Crater Theory," which assumed that volcanoes were pushed up in much the same manner as is the cuticle in the formation of a blister upon the body. Like the theory of the Neptunists, this doctrine was overthrown as soon as inductive methods of examination were applied to it.

Two doctrines of geology which were destined to play a large rôle in the history of science were developed in France. The "pentagonal network" theory of Elie de Beaumont furnished the age of every range of mountains from the direction of its trend referred to the cardinal points; while the cataclysmic theory of Cuvier held that the earth's history had been punctuated by great cataclysms resulting in the destruction of all life upon the globe and followed always by a recreation of new faunas and floras. These doctrines, like those emanating from Germany, were destined to succumb to the rigid tests of the observational methods.

The control of scientific theory by the Church whenever it felt that its doctrines had been invaded was, if less formal and direct, none the less potent even as late as the latter half of the nineteenth century. This became apparent so soon as attacks began to be made upon the theory of catastrophism, for this theory was regarded as harmonizing with the biblical account of the creation. The evidence for the overthrow of this doctrine had been long collecting by a group of giants in science which developed in England toward the middle of the nineteenth century and which included Darwin and Huxley, Wallace, Lyell and Hooker. In the field of geology Lyell's theory of uniformitarianism was the counterpart of evolution in the organic world.

The battle was joined in 1859 with the appearance of the "Origin of Species," and it was fortunate for the scientific world that

the crisis brought to the front a Huxley who could face "such a storm of wrath and flood of contumely as might have overwhelmed a less resolute and clear-headed champion." Gifted with a clarity of thought and expression and a vigor of utterance which are without a parallel in the whole field of science, Huxley had an utter contempt for dishonesty in thinking and little patience with mere metaphysical abstractions. To his friend Kingsley in one of the most remarkable of all his writings he says:

I have champed up all that chaff about the ego and the non-ego, about noumena and phenomena, and all the rest of it, too often not to know that in attempting even to think of these questions the human intellect flounders at once out of its depth.

He correctly gauged the nature of the struggle which was coming and to Darwin he wrote on the appearance of the “Origin of Species":

I trust you will not allow yourself to be in any way disgusted or annoyed by the considerable abuse and misrepresentation which, unless I greatly mistake, is in store for you. Depend upon it, you have earned the lasting gratitude of all thoughtful men. And as to the curs which will bark and yelp, you must recollect that some of your friends, at any rate, are endowed with an amount of combativeness which (though you have often and justly rebuked it) may stand you in good stead. I am sharpening up my claws and beak in readiness.

It was not long before the stage was set for one of the most dramatic moments in the history of science, for the British Association for the Advancement of Science was to meet at Oxford in 1860, and it had been given out that the Bishop of Oxford had determined to "smash" Darwin. The meeting place in the medieval university building was in consequence crowded to suffocation with even the window ledges occupied by university dons keen for the excitement of the contest. By a mere accident and at the last urgent request of his friends Huxley reluctantly agreed to be present, for he