same paternal Hand which originally called their powers into action.

FIRST WEEK-TUESDAY.

ON THE INTERNAL HEAT OF THE EARTH.*

BESIDES the phenomena already alluded to, relative to heat, there is another of very extensive operation, which, although it cannot be considered as entering immediately, in any perceptible degree, into the formation of climate, is yet too remarkable to be passed over without some notice. I allude to the existence of that heat in the interior of our globe, which cannot be referred to external causes, and which has produced, and is continually producing, great and important changes on its surface.t

Indications of the action of a powerful heat in the inner strata of the earth, meet the geologist at every step of his investigation, and it is only by this agency that he is able to account for various existing phenomena at or near the surface, from which, instead of stopping to enumerate them all, I shall select a few of the most striking instances.

*For several of the facts stated in this paper, I am indebted to a valued friend.

"The evidence in proof of great and frequent movements of the land itself, both by protrusion and subsidence, and of the connexion of these movements with the operations of volcanoes, is so various and so strong, derived from so many quarters on the surface of the globe, and every day so much extended by recent inquiry, as almost to demonstrate that these have been the causes by which those great revolutions were effected; and that, although the action of the inward forces which protrude the land has varied greatly in different countries, and at different periods, they are now, and ever have been, incessantly at work in operating present changes, and preparing the way for future alteration in the exterior of the globe."-Fitton's Geological Sketch : See, also, Lyell's Geology, vol. i. passim. This author observes, that the subsidence occasioned by volcanic agency, is somewhat greater than the elevation, and that the climate has been much affected indirectly by the changes thus produced in the relative position of sea and land.

These

Two kinds of springs exist in Nature, the common, and the thermal or warm. The temperature of the common spring is found to be nearly that of the medium temperature of the locality where it rises; the thermal spring possesses a considerably higher degree of heat. The temperature of the former is derived from the soil heated by the sun; the latter, from the heat of those internal strata, from whence they issue. The thermal springs vary in their temperature from a single degree above the medium of the climate, to the heat of the warm waters of Bath, and the boiling Geysers of Iceland. springs are to be found in almost every country, and exist to an extent which has not yet been ascertained. Artesian wells are almost universally thermal; and it is a strong proof of the existence of a high temperature in the interior of the earth, that the heat of these wells increases in proportion to the depths at which they take their rise,—a fact which seems to be ascertained on satisfactory evidence. It is also worthy of remark, that thermal springs do not belong exclusively to any particular formation, being found in the latest as well as in the oldest series. They exist below the level of the sea, and at all heights above it, to the extent of 12,000 and even 13,000 feet. They are discovered in all latitudes,in the neighborhood of the polar regions, as in Iceland and Greenland, equally as in the temperate zone, and under the equator. Their heat cannot, therefore, be sought for in any particular formation of rocks, nor in local chemical processes, but in some cause which is of very extensive operation throughout the interior of the earth.*

In connexion with the fact, that the temperature of Artesian wells indicates the depth of their formation, I have to observe, that, in all mines, it has been lately ascertained, that the temperature increases as we descend. The exact proportion of increase for the descent, has not yet been very accurately settled; but by collating the observations already made, it may be safely stated at 1° of heat for every forty-five feet of descent.

* Bischof.

The last and most decisive proof of the existence of internal heat, is to be found in the volcanic agency, which appears in every age to have been actively and extensively employed, and so many traces of which have been left in every part of the world. Mr. Lyell informs us, that there are certain very extensive regions, to which both volcanoes and earthquakes seem chiefly to be confined, and which would appear to be connected with immense internal fissures in the crust of the earth, through which the central heat finds its way to the surface. He particularizes the whole region of the Andes, including Mexico and the West Indies, which pursues a course of several thousand miles, from north to south; the region, of at least equal extent, which commences on the north with the Aleutian Isles, and extends first in an easterly direction, for nearly two hundred geographical miles, and then southward, without interruption, throughout a space of between 60° and 70° of latitude, to the Moluccas, where it branches off in different directions; and, in the Old World, the region extending from the Caspian Sea to the Azores, a distance of about 1000 geographical miles. "Over the whole of the vast tracts alluded to," says this author, "active volcanic vents are distributed at intervals, and most commonly arranged in a linear direction. Throughout the intermediate spaces, there is abundant evidence that the subterranean fire is at work continuously, for the ground is convulsed, from time to time, with earthquakes; gaseous vapors, especially carbonic acid gas, are disengaged plentifully from the soil; springs often issue at a very high temperature, and their waters are very commonly impregnated with the same mineral matters, which are discharged by volcanoes during eruptions."*

The fact, then, seems to be established, that there is a vast region of excessive heat in the centre of the earth; and that the crust of the globe is rent internally into very extensive fissures, along which that formidable agent approaches nearer the surface, and through which it finds

* Lyell's Geology, vol. i. p. 360, &c.

This, being proved,

occasional or permanent vents. seems to open to us, not only one of the natural causes of the previous revolutions on the surface of our planet, but a source of future disruption and ruin. The "more sure word of prophecy" informs us, that the time will come when the elements shall be dissolved with fervent heat, and the earth, and all that is therein, shall be burned up; and geological indications render this catastrophe not only possible, but probable. Let it only be conceived that the safety-valves, by which the superabundant heat generated internally is at present thrown off, were by some convulsion to be stopped up, or that some other deranging cause were to occur, which should destroy the equilibrium at present subsisting between the great central fire and the shell in which it is enclosed, and a force would be exerted, which might altogether derange the present system of things, and set the world in a blaze. The powers which sustain the great planetary system, are equally balanced, and, notwithstanding the existence of a resisting medium, may, as to all practical results, be considered stable; but it is not so with the materials of our own globe. These have already undergone numerous disruptions; and there is one other catastrophe still in reserve for them. We see the elements of that catastrophe in existing phenomena, and, when we look to the announcements of Scripture, the event, which might almost be anticipated, seems to be foretold.

The friend who was so obliging as to furnish several of the above-mentioned facts, takes much laudable pains in the paper he has sent me, to show that the operation of natural causes in no respect precludes the immediate arrangements of the supreme moral Governor, in carrying on the great schemes of his providence; and that, even if it could be proved that the Deluge, for example, or the destruction of the Cities of the Plain, was brought about in the natural course of events, these ought still to be regarded as catastrophes determined in the councils of the Most High, to bring signal vengeance on his rebellious creatures, and calculated by Him, with consummate wisdom and unerring prescience, to effect a great

moral purpose. Nothing can be more true or important than this sentiment. The world of Nature, and the world of Providence, are always in harmony; and the Eternal brings about his decrees usually by the adjustment of general laws, to the purposes of his moral government ;—and yet He has reserved to Himself the power of interfering with those laws when He thinks fit, that by doing what He alone could perform, He might bear undeniable testimony to the mission of his Son, or to those messages which He was from time to time pleased to send by His servants from the unseen world. In the latter case, the hand of God is discovered by the miraculous nature of the transaction; in the former, by the fulfilment of prophecy. If the destruction of the world by fire, therefore, shall prove to be the result of natural this will not diminish the evidence of Divine agency; for, independent of the miraculous events with which we are assured it will be accompanied, its very coincidence with prophetical intimations will sufficiently evince the source from whence it proceeds.

causes,

FIRST WEEK-WEDNESDAY.

INCREASED LIGHT.

It is not merely the increase of heat, but the increase of light, which constitutes the peculiarity of summer weather. The latter property is almost as necessary to organized life as the former, and its abundance at this season, produces, doubtless, an important effect both on the vegetable and animal world. In another volume, I have alluded to the uses of light in the growth of plants,* and have particularly noticed the power which it possesses of endowing them with smell, color, and inflammability, as well as the essential function which it exercises in respiration through the leaves, where the proper juice

*Spring,' pp. 71–73.