Part 3

The fifth, sixth and seventh theories are mere hypotheses, unsupported by either demonstration or observed facts.

The eighth has been presented to the scientific world through the labors and researches of that eminent geologist and physicist, Dr. James Croll, in his various articles in leading scientific magazines, and lastly, in his grand contributions to the subject under discussion, “Climate and Time” and “Climate and Cosmology.”

The ninth has been maintained by one of the greatest English naturalists, Mr. Alfred Russell Wallace. He combines the theory of Dr. Croll with that of Sir Charles Lyell, and very ably presents his views in “Island Life.”

The tenth is a presentation by Dr. Ball, F. R. S., etc., of an interesting demonstration, to the effect that 63 per cent. of solar heat reaches either hemisphere during its summer exposure, and the remaining 37 per cent. during winter exposure. Nothing is added to the Physical Theory of Dr. Croll, nor does the demonstration in any way remove the serious objections which have been urged against Dr. Croll’s views.

The strongest support that has been given to any of the above theories is made by the arguments and deductions of Dr. Croll and Mr. Wallace; yet they have failed to produce conviction, for, in a recent work on Geology, the author, after reviewing the various theories as to the cause of the Glacial Period, uses this expression: “This seems to be by far the most probable yet presented.”

This opinion is directly given upon only one--the ninth; but its terms are such that it embraces all. If the ninth is “by far the most probable,” it would be difficult to fix the degree of probability or improbability of the others.

The only explanation which can be accepted is one which will admit of definite proof, and will satisfy all the conditions, and not require the distortion of known facts, by forcibly fitting them into arbitrary molds. It must start from universally admitted premises, and in rigid consonance with known laws, correctly interpret the grand eras of climate which have marked the geological history of our globe, and further, it must point out and fully elucidate wherein and why the present climates of our globe differ so radically from those vast secular variations recorded by fossil life--aye, more, it must be so general as to be of universal force and applicable to other members of the solar system constituted as our globe.

In the brief review just made of the principal theories urged by various scientists as causes producing the Ice Age, it was remarked of the first that it was universally admitted as true, and even taught in elementary works on Physical Geography, but that it failed to account for all the facts developed by the Ice Age. This first theory was a decrease in the original heat of the globe, the truth of which is established by a mass of indisputable geological evidence.

The present conditions are so radically different from any of the eras of climate known to have existed, that the explanation of this range of secular changes becomes the grandest problem in terrestrial physics, and has an important bearing in the solution of existing conditions upon the other planets.

It is universally admitted that this original heat has been so lost that it is no longer a factor in the surface temperature of the earth, and that solar energy is now the controlling source of heat.

There can then be no mistaking the first nor the present condition of the earth as regards its exposure to the only two sources of heat--(1) solar and stellar heat, and (2) resident, internal, or earth heat. There can therefore be no error as to the main features of the problem.

There must have been two marked eras of climatic control--(A) a past era, during which both sources were active; (B) and the present era, in which the greater exterior source only remains, the local and lesser source having been practically exhausted.

Or, in other words, we have, first, a heated globe having resident in its mass a finite quantity of heat, undergoing loss and exposed to an exterior source of heat and light, which source may be either constant or decreasing in its energy, but so slowly that it may be considered sensibly constant during the eras under consideration; second, the same globe deprived of its heat to such an extent that a crust of non-conducting material has formed, the outer surface of which is exposed only to solar heat, and whose climates are entirely controlled thereby. The objects in view being to explain (1) the peculiar uniformity of climates prior to the exhaustion of the first source, and (2) the occurrence of an age of general glaciation in all latitudes prior to the establishment of the sole control of the exterior source; (3) the reasons of the differences between heat distribution during geological and present climates. Such explanations to be in strict conformity with admitted facts and known laws, and without omitting the one nor distorting the other.

To be explicit we will state that the prime objects are to demonstrate--

1. That in the passage of the earth from an era during which its climates have been controlled by internal heat into an era during which its climates are controlled by solar heat, eras of uniform climates must have been passed through during which isotherms were independent of latitude.

2. That before climates could have passed under solar control that an age must occur during which continental areas must be glaciated; and that this stupendous phenomenon, occurring before solar climatic control, was also independent of latitude.

3. That the direct cause of the Ice Age was a combination of the remarkable properties, in relation to heat and cold, possessed by the various forms of water. As vapor, in the form of fogs and clouds it prevented the loss or receipt of heat by radiation; as water, by reason of its high specific heat, it retained to the last moment the effective remnant of earth heat; as ice, it assumed a solid form, storing the maximum amount of cold.

4. To point out in a general way the fallacies of previous attempts to explain geological and present climates.

The problem will be given in a general proposition, which is capable of demonstration in perfect accord with known laws.

THE GENERAL PROPOSITION.

GIVEN.--A heated globe, constituted and circumstanced as the earth, and whose surface temperatures, by reason of internal heat, are above the boiling point of water, to prove that before its surface temperatures can pass under the control of the solar heat (1) that climatic changes must be independent of latitude, and (2) that the continental areas must be glaciated.

It will be observed that the surface temperatures of a globe thus situated are entirely controlled by its own internal or earth heat; for between such surface and any external source, a dense cloud of vapor must exist. The fact that direct or radiant heat rays cannot pass through dense fogs and clouds is well known; therefore, a globe thus situated can neither give off, nor receive radiant heat. The peculiar function of solar heat during the existence of appreciable quantities of earth heat was to warm the upper regions of the atmosphere and the outer surface of the clouds exposed to its power, thus partly replacing the heat lost by radiation into space, and causing the store of earth heat to last longer.

By the conditions of the problem presented, we thus have a globe having resident in its mass a finite quantity of heat exposed to loss only by means of the gradual expansion of water into vapor, and the exposure of this vapor to loss of heat by radiation from its upper surface into space. This vapor would then condense, and as rain, snow or hail, descend all, or part of the way to the earth, receive another increment of heat, and ascend as before. A slow process, but exhaustive in time.

Thus the property of water to assume three forms, each of which possesses remarkable qualities with regard to heat and cold, afforded the only means for exhausting the earth heat. As vapor, it possesses the property of storing more heat than any other known substance; as snow or ice it possesses the property of storing more cold than any other known substance. The function of solar heat, until the exhaustion of earth heat by this process, was simply conservative; it merely warmed the upper layers of the atmosphere, through whose dense vapor its heat rays could not pass. Clouds being more translucent than transcalent, light rays reached the planetary surface prior to heat rays.

The earth may thus be regarded as having been surrounded by a series of spheroidal isothermal shells of mean temperatures. The one next the surface represented a mean temperature of 212° + t° Far.; t being positive, and proportioned to the greater pressure of the heavier atmosphere existing. Above this isothermal shell were others representing mean temperatures of 90°, 60°, 32°, Zero, etc., to -x° Far., the extreme cold of interplanetary space. Between the two spheroidal isotherms of 32° and -x° Far., was one which had a mean temperature of 32° - y°, and equally exposed to both sources of heat.

That the spheroidal isotherm of 32° Far. was within the sphere of influence of earth heat, is proven by the formation of snow or ice at that temperature, both being the resultant of vapor expanded and raised by earth heat to that height as a minimum. Moreover, vapor would have reached that height as a minimum were solar and stellar heat suspended for a definite period, and the earth absolutely exposed to loss by radiation with no partial return of heat, from exterior sources.

It therefore follows that the isotherm equally heated by both exterior and interior sources was colder than 32° Far. or below that temperature at which snow and ice form. (It is well known that solar energy cannot maintain a temperature as high as 32° Far. except in the lower regions of the atmosphere.)

The isothermal shells nearest the earth were spheroidal in shape, and by reason of the conditions their surfaces were practically parallel with that of the earth; those most remote from the earth, by reason of solar influences, protruded at the equator and flattened at the poles, so as to be slightly more oblate than the earth; they were sensibly parallel with the spheroidal isotherm now marked by the “snow line.” Hence at the equator the direct action of the sun was first felt and established.