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maximum height in the sky. During the midsummer months the sun would acquire considerable heating power, and this power would be so constant, and free from diminution by nocturnal cooling, that the land and waters would become warmed, and would absorb heat. This heat would be gradually liberated later in the year. The local distribution of heat would be modified by the nature of the ground, the height of land, and the distribution of sea and land; but it is theoretically probable that at the Pole the mean temperature of the air in July and August is much higher than it is generally thought to be. During the winter the continuousness of the night would equally favour a very low temperature, so that probably the range of temperature in the circumpolar area is greater than in any other part of the globe. Evidences of high summer temperature are not entirely wanting. Many of the most northern coasts reached are strewed with drift-wood, and even trunks of trees, which in many cases appear to have come from the north. A list of the species thus occurring would throw light upon the probable localities where they grew. Again, streams or outflows of warm water from the Pole have been observed in many localities.

These, wherever met with, are commonly assigned to the Gulf Stream; but as will be noted in a subse

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quent chapter, the warm water originates at the Pole. This is a question which requires investigation. There are many other questions connected with Polar temperature of a very complicated and involved character, which cannot be fully entered into here. One or two may be alluded to. It is known that the mean temperature of the Southern hemisphere is lower than that of the North; and it is a matter of observation that the Antarctic Pole is more extensively ice-clad than the Arctic. This may be in part conjecturally explained by the greater extent of land at the South than at the North Pole. It is also known that the earth revolves round the sun in an elliptic orbit, so that it is at one time nearer the sun than at another. At the present time the Poles are farther from the sun in summer and winter than in spring and autumn. It has already been indicated that the North Pole is warmed up during the summer, and as the warming of the South Pole occurs under similar conditions as regards heat, &c., the South Pole should have a similar temperature whereas it is the coldest. This is probably indicative of the North Pole being for the most part surrounded by water. During the spring the heat is being gradually increased by the gradually increasing height of the sun, which increase is in part counterbalanced by the

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recession of the earth from the sun, while in autumn the decline is in part counterbalanced by the earth approaching the sun. This would help to raise the autumn temperature. If the northern summer occurred when the earth was nearest the sun, the circumpolar area, it is believed, would be heated more strongly than it is now. The intensity of the heat might be still further increased by another modification of conditions. The present eccentricity of the earth's orbit is slight compared to what it has been in past times. At present the earth is 3,000,000 miles less than the mean distance nearer the sun in aphelion than in perihelion; but at certain periods it has been 14,500,000 miles less than the mean nearer the sun in aphelion than in perihelion. In other words the earth when nearest the sun is now about 88,400,000 miles from the sun; but during past epochs it has approached to within about 77,000,000 miles. The intensity of the heat is in inverse proportion to the square of the distance : so that if the Arctic Pole were exposed to this greater heat during summer, the temperature, other conditions remaining the same, would be proportionately increased. There is yet a third modifying cause which would tend to intensify the heat. The obliquity of the ecliptic is now 23° 28'; but astronomers

admit that it may have been at times as much as 30°. This would imply a more extensive Arctic circle, and a higher, therefore a hotter, sun during the midsummer months. It is possible to conceive a time when the Polar regions were under the most favourable conditions as regards heat-a time when the earth was at its nearest to the sun in midsummer when the Polar region contained little or no land, and when the sun rose high in the heavens, shining for weeks or even months with noon-day power. At present the conditions are for the most part not the most favourable for warming the North Pole; and the fact that it is less ice-encumbered than the South Pole probably arises from there being, as is supposed, little land near it. The conjectures above given as to what may have been are rendered probabilities by the character of the fossil plants which have been discovered in high latitudes. On Bear Island has been found the earliest rich land flora as yet known. Its age is assigned to the beginning of the Carboniferous epoch, or the later portion of the Devonian epoch. This flora comprises species of Calamites, Lepidodendron, Cyclostigma, and many ferns. The individual specimens are exceedingly abundant. The flora has been traced from 47° to 76° N. A flora of a somewhat similar character occurred in Parry Island

and Spitzbergen at a somewhat later period, represented by the mountain limestone. Further research will probably indicate its occurrence in other northern countries. The bearing which these facts have on climate is thus expressed by Professor Heer: "Moreover the climate of Bear Island must have been as favourable to the growth of plants as that of Ireland or the Vosges, although that island lies 26° farther north; for the corresponding species are as large and quite as luxuriantly developed, and have even produced more considerable coal strata than those of lower latitudes in the same period. Warmth, therefore, must at that time have been more equally distributed over the earth, whilst already in the Miocene time a great difference had begun to arise, which has increased immensely up to the present time. The climate must have been not only more equable but warmer, as is shown by the coral banks which were formed at that time in Spitzbergen, as well as by the enormous tree-like cryptogams, and the large-leaved ferns which Bear Island produced." In Greenland fossil plants belonging to several periods have been discovered. Those from Angiarsuit and Kassok are very old, but the age has not been determined. They however seem to be similar in character with those from the lower cretaceous beds at Korne. At