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second, when an eclipse will occur, if it should be thousands of years hence, it is taken for granted that all they teach must be true! But while a child

may

look to the dial of a timepiece, and tell us to a second when the pointer will cover a certain mark, not one among ten thousand of grown men can go behind the dial, and explain how the causes operate by which the hands or pointers are moved. So may a very poor thinker calculate the time of a transit, or an eclipse, while the loftiest intellect becomes bewildered, and is lost in trying to prove even the existence of those forces on the reality of which the fundamental doctrines of physical astronomy depend. The noblest minds are overtaxed when honestly attempting to tell us whether there is such a thing as centrifugal force, and what it really is, which is called "gravitation.” No one has gone behind the scenes, and seen how the highest authorities in astronomy are situated, without seeing that the physics of this science are as unsettled and uncertain as those of geology itself. But we gladly look into its, teachings notwithstanding:

Mr. Croll, of the Glasgow Andersonian University, has presented the world of science with the best phase of one of the most interesting of all theories from this quarter.* Sir Charles Lyell has given Mr. Croll great credit for his labours in this matter, as one who has pointed out a real cause hitherto neglected in the calculations of geologists; and although we cannot accept the conclusions at which he arrives, we must acknowledge our admiration of this writer. His idea, in essence, may be briefly stated. Our globe in being carried round the sun, as modern astronomy teaches, has a path which is not a circle, but an ellipse. This, of itself, causes the earth to be nearer the sun in certain parts of its orbit, and farther away in others. But this elliptical path of the earth does not always maintain the same relation to the sun as a centre; it changes continually, and in the course of time, the aggregate of change is very considerable. At one time, the earth, at its nearest approach to the sun, is vastly nearer, and, at its farthest departure, vastly farther from that source of heat than it is at other times. The difference, as it is calculated by astronomers, is expressed in millions of miles. This element alone, however, would not give us any reason which could account for a change of temperature on the surface of the globe, because the motion of the earth being quickened in proportion to the nearness of its path to the sun, the amount of heat which it receives is the same when it is nearest as when

* See the Reader for October 14th and December 2nd and 9th, 1864; also Philosophical Magazine, 1866, pp. 26, 27, 28, and 30.

it is farthest from the solar centre. But there is another element which combines with what is called the eccentricity of the orbit. Winter and summer are not caused by our being farther from the sun in the one than in the other ; but by that motion of the earth which shortens, or, as we may say of polar regions, blots out the winter's day, and lengthens the day of summer. In polar latitudes, the sun shines on the surface of the globe during the whole twenty-four hours of the summer's day, and is not seen at all in winter. It is on the effect of this, which arises from the turning away of the polar surface from the sun, that Mr. Croll chiefly depends for the proof of his theory. The radiations of heat must be excessive from the polar surface, when it is dark and at its greatest distance from the sun—when, too, because of its slow motion, its winter is at the longest. This loss of heat (as Mr. Croll argues) will not be compensated by the sun's nearness in summer; for the shortness of that season, from the swiftness of the earth's motion, in proportion to the length of the winter, will prevent all that would otherwise make the summer warm. Put, then, these two things together-let the northern winter occur when the earth is farthest from the sun, and, consequently, the summer when it is nearest—the winter will then be excessively severe, and the short summer, not even usually warm. This, Mr. Croll thinks, will cause a glacial period over great part of the northern hemisphere. Now, let the case be reversed—the short winter occurs when the earth is nearest the sun in space, and the long summer when it is farthest away.

The consequence of this will be greatly lessened radiation in winter, and the equalizing, to a great extent, of that season and the summer in northern regions. These opposite combinations of the earth's position, in relation to the source of heat, account, according to this view, for regularly recurring periods of extreme winter cold, combined with proportionally small summer heat, such as will fail to melt the winter snow, and periods when the summer and winter are lost in constant spring. Could we confine our reasoning to astronomical theory, and leave out other considerations of a geographical nature, Mr. Croll would, we think, make out a pretty strong, case by his argument for a glacial period,during the time when the winter occurs at our greatest distance from the sun. But this is not the problem which is of greatest importance, as we are constrained to view the case, —that has respect to a hot climate sufficient for palms and turtles in our northern latitude. Mr. Croll does not attempt to make out this. He has difficulty in making out a period fit even for the ferns of the coal-measures, when winter occurs

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at our nearest to the sun in the earth's eccentric orbit. He argues only for a "perpetual spring.” His mean temperature, calculated for Great Britain, is only 60° F. This, he argues, must have been the summer and winter heat, with scarcely any variation, in the Carboniferous period. But, as we have seen, geology calls for the climate of the hottest parts of India, an equatorial climate whose mean heat is 81o. What we want is, at least, a tropical climate in the latitude of London—a climate very different indeed from that which, even according to revised ideas, could suit the vegetation of the Coal period. In thinking of the possibilities of such a climate in the North, it is necessary to keep in mind the truth to which we have already referred, that the length of the polar summer's day, though giving great advantage in the reception of heat by the constantly enlightened parts, presents only a slanting face to the sun, and so can never account for the heat and other effects which flow from the vertical radiance of Bengal. Sir Charles Lyell, in criticising Mr. Croll's theory, quotes from the Encyclopædia Britannicu, the results of the reasoning there given in the article on climate. It is to the effect that the sun's rays passing through the atmosphere, so as to fall on the earth's surface at the equator, give 115° of heat, for 51° given in latitude 45° south or north, and for 14° given at either pole.* The latitude of the London clay is 51° 30' N. The radiance of the sun, which gives 115° F. at the equator, and gives only 51° as far as 45° north latitude, is required to give an equatorial heat more than six degrees further north than where it can give only 51o. How will Mr. Croll, or any one else, make this out, and so explain on this theory the tropical remains in the isle of Sheppey? Yet this is that for which an account is required as the facts of geology stand.

The remains which, as we have seen, are imbedded in the London clay and kindred formations, are such that nothing short of the sun's vertical radiance will account for them. Dr. Hook saw this as early as 1688, and although his idea has been scouted, it is not on that account the less true. But, in addition to all this, any one who has had to do with the growth of palms and other tropical plants in this country, knows that it is not so much want of heat which renders it impossible to grow them satisfactorily, nor is it the want of moisture. These can be supplied; but what we lack is the sun's tropical radiance. Sunshine means much more than mere heat. How to show that this ever fell on the

* Lyell's Principles of Geology, vol. i., edition 1867, p. 284.

earth, in such a latitude as that of Britain, as it falls now in India, and raised even the ocean to a temperature such as that of the Indian Ocean now, is the problem which we think astronomy, as generally understood, cannot solve.

Even if we grant the truth of the fundamental principles on which the calculations of the first philosophical astronomers of our time are based (and many competent thinkers will not grant so much), we are totally without anything in the popular teachings of the science that accounts in any degree for the facts of geology to which we refer.

In coming to a conclusion,* we are very forcibly reminded of a saying of one great man of science, which has been quoted and applied to a special idea by another of nearly equal standing. We direct attention to it, because it falls so signally short of the whole truth, and yet so faithfully represents a part of that truth. It fails to express that very thought which is of greatest moment as science stands at the present day. Agassiz has said, “ that whenever a new and startling fact is brought to light in science, people first say, 'It is not true;' then,' It is contrary to religion ;' and, lastly, that 'Everybody knew it before.' Sir Charles Lyell quotes this in reference to the idea of the former existence of man with many extinct mammalia, holding that this, which he seems to regard as a “fact,” has gone through all the three stages spoken of by Agassiz, at least so far as practical geologists are concerned. This idea of the coexistence of men with mammoths, it is important to observe is not a FACT, even if perfectly true. It is only an inference, at best, perhaps a theory by which certain facts are partially explained. So far as this matter of coexistence of man with extinct species of animals is concerned, we are not anxious as to what may prove to be its ultimate development. We refer to it at present only in connection with the idea of the three stages through which Agassiz said a new and startling fact passes. Such "facts” are often only theories, and we think we have given abundant evidence that the law of such things in geology calls for a fourth stage, which follows the three thus mentioned. In this fourth stage, “people” believe and teach the startling doctrine for a generation or two, and then find out that they have been all the while thoroughly deceived ! Let any one pass carefully over the ground at which we have but glanced in this paper, and then let him say if the vast

* In preparing this paper I have left out of sight not a few of the speculations by which geology has come into conflict with the Bible, partly because moderate limits had to be studied, and also because I was desirous not to repeat here what I have published already.

majority of ideas that have prevailed in the geological mind have not passed already through all these four stages.

What, then, are the relations of geological science, as popularly understood, to the Sacred Scriptures? They are the relations of that which in its fundamental principles has been changing, we might almost say, every hour of its history, to that which has passed down through thousands of years, running the gauntlet between the ranks of ten thousand times ten thousand assailants, remaining unchanged and even untouched to the present moment. So far as the facts and certain inferences of geology are concerned, they do not in any degree affect the Sacred Scriptures. The vast ages that have been made to occupy the minds of men when thinking of the world's history, and are now multiplied into endless millions of years, belong all to that conjectural thought which, as we have seen, is so perpetually changing: Few things are so fitted to humble us as an honest admission of our weakness under the influence of this. Men have thought that they were forced to remodel their ideas of the word of God, and even to abandon the belief of its Divine inspiration, by the force of that which turns out to be only a shifting dream! So we see the wisdom of those who have said to us, as they held back themselves, “Allow your Bibles to remain as they are ; wait awhile, till it is seen what these speculations are worth. We have been too often misled by such conjecturings to be in any hurry to acknowledge their weight.” And we see now our own well-meant folly, mingling with that of many others, in labouring to construct Scriptural theories that might harmonize with the passing visions of the scientific mind. As the men of science and the men of Scripture—the geologists and the theologians—awake together from their reveries, it seems as if it were to find, as we have already hinted, that the teachings of Moses regarding the world's uprearing are, after all, the grandly comprehensive truth-in very deed the Word of the Living God.

The CHAIRMAN.—It would be a mere idle form for me to ask you for a vote of thanks to Professor Kirk for the interesting and valuable paper he has just read. I am sure no one who has heard it found it too long; our only regret must be, that we had not the time to listen to, and Professor Kirk the physical power to have delivered, one double the length. There are few outsiders of Geology (as Professor Kirk has characterized himself) who have paid any attention to the subject, who will not feel that the Professor's greatest difficulty in writing his paper, must have been in selecting the few baseless theories he has spoken of this evening from among

the many

whose

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