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Show 116 CAUSES OF water of. great depth, which could not readily be reduced to the freezing point. The same opinion is farther confirmed, when we compare the quantity of land lying between the poles and the 30th parallels of north and south latitude, .and the quantity placed between those parallels and the equator; for it is clear, that at present we must have not only more than the usual degree of cold in the polar regions, but also less than the average quantity' of heat generated in the intertropical zone. In order to simplify our view of the various changes in climate, which different combinations of geographical circum.. stances may produce, we shall first consider the conditions necessary for bringing about the extreme of cold, or what may be termed the winter of the ''great year," or geological cycle, and afterwards, the conditions requisite for producing the maximum of heat, or the summer of the same year. To begin with the northern hemisphere. Let us suppose those hills of the Italian peninsula and of Sicily, which are of comparatively modern origin, and contain many fossil shells identical with living species, to subside again into the sea, from which they have been raised, and that an extent of land of equal area and height (varying from one to three thousand feet) should rise up in the Arctic ocean, between Siberia and the north pole. In speaking of such changes, we need not allude to the manner in whi h we conceive it possible that they may be brought about, nor of the time required for their accomplishment,-reserving for a future occasion, not only tho proofs that revolutions of equal magnitude have taken place, but that analogous mutations are still in gradual progress. The alteration now supposed in the physical geography of the northern regions would cause additional snow and ice to accumulate where now there is usually an open sea; and the temperature of the greater part of Europe would be somewhat lowered, so as to resemble more nearly that of corresponding latitudes of North America; or, in other words, it might be necessary to travel about 10° farther south, in order to meet with the same climate which we now enjoy. There would be no compensation derived from the disappearance of land in the Mediterranean countries ; for, on the contrary, the mean heat of Clst du meme ordre que la. hauteur moyenne des continens et des iles au-dessus d~ son niveau, hauteur qui ne surpasse pas mille metres (3280 ft.)." Mec. C~leste. Bk, 11, et Syst, du Monde, p. 254, . CIIANGJ~r s OF' TEMPERATURE. 117 the soil so situated is b bl belong to the sea b' hp.roh a ~far above that which would ' Y w Ic we Im C/'. • let the configuration of th £ aome lt to be replaced. But let some large district :t~~r ace be still further varied, and Mexico for example wi'thw~t In or n.ear the tropics, such as twelve thousand fee' t d Is mount ams l'·l s·m g to the heiO'ht of · an upwards b 0 while lands of equal ele t' d ' e converted into sea . . va Ion an exte t ' arctic circle. From this h h n are transferred to the c ange t ere w ld . l result a sensible diminution of tem ou ' m t le first place, the soil of Mexico would l perature near the tropic for no on O'er be h t d b ' that the atmosphere would b l ea e y the sun ; so tic, and the Gulf stream 0 e ~ss warm, as also the Atlan- Europe, Northern Asia ~nd ~ t tf other .hand, the whole of influence of the enormo~ ?r 1 ~menca, would feel the d s quantity of Ice d rate at vast heights on the new . . an . snow, now gene-have already seen, there are som ai~tic ~ontment. If, as we sphere where snow is perpetu 1 : p~m~s m the southern hemitudes as low as central EnO']a:d o t ~e e;el of the sea, in latithe case throughout a grea·~ ' sfuc 1 might now assuredly be extreme limits of drifted . p~rt o Europe. If at present the easily reach the equator aifcte ergls are the Azores, they miC/'ht T er t le chang b o ~pursue the subject still farther 1 es a. ove supposed. tams, with the whole of H' d ' et the Himalaya moun b . m ostan si k d - e occupied by the Ind' ' n own, and their place f . Ian ocean and th I o territory and mountains of ;h en et an equal extent from North Greenland to th'e Ork: sa.me vast height, stJ·etch cult to exaC/'gerate th ey Islands. It seems di'ffi o e amount to h. h - n?rthern hemisphere would now w Ic the climate of the Withstanding the great refriC/' . be co~led down. But, notduced, it is probable that o;~:ti~;~vhiCh would thus be pro~ ure between the arctic and ' :renee. of mean temperaIncreased in a very hi' 0'1 t' e~ uatoriallatitudes would not be b h o 1 ra 10 1or n d' . roug . t about in the climate' of o gr~at Isturbance can be ~mmcdiately affecting all other latit dpar~cular region, without eat and cold which s d u es, owever remote 'l,h t urroun the 1 b . · e :ian~ and universal flux and reflux go ,e are m a state of con-r Is always risin C1' and n . ~ • 'llle Ileated and rarefied poles · h 5 uowmg ll'om th In t e higher reC/'ion c equator towards the lower, the colder air is ii~ . s . of the atmosphere, and, in the That this circulation . wmg back t.o restore the equilibriu 1s constantly C/'omg on · I .. . m. 5 m t 1e aer1al cur- |