16 



POLAR REGIONS. 



Polar vennes ; that the Euxine Sea was frozen over every 



Regions. w i n ter in the time of Ovid ; and that the ice of the 



"*~ v ~"" Rhine and the Rhone sustained loaded waggons : we 



cannot ascribe the amelioration of such climates to the 



influence of agricultural operations. 



" The cold meridian which now passes through Ca- 

 nada and Siberia, may then have passed through Italy ; 

 and if we transfer the present mean temperatures of 

 these cold regions, to the corresponding parallels in 

 Europe, we shall obtain a climate agreeing in a singu- 

 lar manner with that which is described in ancient au- 

 thors. 



" It is not, however, in the altered condition of our 

 atmosphere merely, that we are to seek for proofs of a 

 periodical rotation of climate. The impressions of the 

 plants of warm countries, and the fossil remains of 

 land and sea animals, which could exist only under the 

 genial influence of the temperate zone, are found dis- 

 persed over the frozen regions of Eastern Asia ; and 

 there is scarcely a spot on the solid covering, of the 

 globe, that does not contain indications of a revolution 

 in its animal and vegetable productions. 



" This interchange of the productions of opposite 

 climates, has been ascribed to some sudden alteration 

 in the obliquity of the ecliptic, and even to a violent 

 displacement of the earth's axis ; but astronomy rejects 

 such explanations, as irreconcileable with the present 

 condition of the system, and as incompatible with the 

 stability of the laws by which it is governed." * 



In temperate and frigid climates, where the temper- 

 ature is liable to sudden and considerable variations, we 

 find the pressure of the atmosphere, as indicated by 

 the barometer, to be also liable to rapid and great fluc- 

 tuations. But as these fluctuations in the spring and 

 autumn, when they are probably the greatest, have 

 been little -observed, we shall only mention the fact re- 

 lating to this part of our subject, that the greatest 

 changes of temperature and pressure often happen si- 

 multaneously, and are generally attended or followed 

 by storms. 



. In proportion as we recede from the equator, we 

 find the climate, as we have already observed, more 

 changeable. This is the case as regards temperature, 

 atmospheric pressure, and winds ; the latter becoming 

 more irregular, variable, and partial, as we approach 

 the frigid zone, or the borders of the polar ices. Thus, 

 at certain seasons, storms or calms repeatedly alternate, 

 without warning or progression ; forcible winds blow 

 in one place, when at the distance of a few leagues gen- 

 tie breezes prevail ; a storm from the south, on the one 

 hand, exhausts its impetuosity upon a gentle breeze, 

 blowing from off the ice on the other, without prevail- 

 ing in the least ; ships within the circle of the horizon 

 may be seen enduring every variety of wind and wea- 

 ther at the same moment; some under close-reefed 

 topsails, labouring under the force of a storm ; some 

 becalmed and tossing about by the violence of the 

 waves ; and others plying under gentle breezes, from 

 quarters as diverse as the cardinal points, t The cause 



of the principal of these phenomena is to be found in Polar 

 the frigorific influence of the ice, in producing unequal Regions 



temperature in the air. They have, however, been only * 



observed early in the spring and late in autumn, the 

 winter and summer seasons being less irregular; and 

 they only occur to their greatest extent near ice or land, 

 and not in the main open ocean. As the sudden storms 

 are particularly dangerous to the arctic navigator, it is 

 of importance that he should be aware of their ap- 

 proach. The best indication is the barometer, which 

 seldom or never fails to predict such gales. But there 

 are other tokens, which are pretty certain. The most 

 general preliminaries to these storms are perfect calm, 

 or curiously variable breezes with strong squalls, and 

 singular agitation of the sea ; together with a heavy 

 fall of thick snow ; often changing from flakes to pow- 

 der, and occasioning an astonishing gloominess and ob- 

 scurity in the atmosphere. "If the snow suddenly 

 clear away, the gale is often at hand, whilst a peculiar 

 luminousness in the horizon sometimes points out its 

 direction, and a noise in the upper regions of the atmo- 

 sphere announces its approach. Some examples of the 

 phenomena attendant on sudden storms are given by 

 Captain Scoresby, in the work we have so often quot- 

 ed. One or two of these we shall extract. 



" In the evening of the 5th of April, 1811, latitude 

 70 49' N. and longitude 7 15' E. the wind blew a 

 fresh gale from the northward, and the barometer, 

 which had been stationary for thirty-five hours, stood 

 at 29.88 inches. At noon, on the following day, we 

 had a moderate breeze of wind from the north west, 

 which, towards evening, increased to a fresh gale, ex- 

 ceedingly variable and squally, accompanied by thick 

 showers of flaky snow. At 9 A. M. the thermometer 

 stood at 10, at 4 P. M. it had risen, to 17, and at 6 

 P. M. to 27. This remarkable rise of 17 of temper- 

 ature in nine hours, indicated a southerly or easterly 

 wind ; and, because the barometer had fallen to 29.50, 

 a severe storm was expected. Since the barometer 

 stands highest on easterly winds, had it remained sta- 

 tionary we should have expected a storm, on the veer- 

 ing of the wind from the N. W. to the opposite quar- 

 ter; but when this change was preceded by a fall of 

 near four-tenths of an inch in the column of mercury, 

 a violent gale might be anticipated. 



" I now walked the deck, somewhat alarmed at the 

 awful appearance of the sky, in the short intervals of 

 the showers. At one time a luminousness resembling 

 the ice-blink appeared in the horizon, extending from 

 the N. N. E. to the E. S. E. It did not, however, pro- 

 ceed from any ice, as I was afterwards perfectly satis- 

 fied ; neither was it likely to arise from the effects of 

 the sun, as it was in a different quarter. 



" In the midst of a thick shower, the snow was ob- 

 served to clear away to leeward, which warned me of 

 an approaching shift of wind. Immediately all hands 

 were ordered on deck, to attend the sails, and every 

 man at his station awaited the event. In about ten 

 minutes the sails gave a violent shake, and were the 

 next instant taken flat aback. The wind, though blow,- 



* Dr. Traill, of Liverpool, in a recent ingenious investigation on the principles and phenomena of thermo-magnetism, submitted tq the 

 Royal Society of Edinburgh, maintains principles not only similar to those of Dr. Brewster, but applies them to the explanation of the 

 change of position in the isothermal poles. Dr. Brewster inferred from the phenomena of temperature, that the present coincidence of the 

 magnetic and isothermal poles is not an accidental circumstance^ but a necessary consequence of some law or principle of nature. Recent 

 discoveries are greatly in support of this idea ; for it is clearly shown, that magnetic properties are developed in almost all bodies by unequal- 

 ly heating them. Hence Dr. Traill, with great propriety, atgues that the earth itself is a great thermo-magnetic apparatus, the properties of 

 which are developed by the disturbance of its equilibrium of temperature, by -the perpetual action of solar heat on its equatorial regions, 

 and the icy covering of its poles. From this principle it would be reasonably deduced, that any change taking place in the poles of cold 

 ought to produce a corresponding change in the magnetic poles. 

 -f Scoresby's Account of the Arctic Regions, vol. i. p. 39T. 



