44 INTENSITY OF SUN'S HEAT AND LIGHT. 



to the outer limit of the atmosphere, upon which the sun shines continually, but 

 from a low altitude which cannot exceed 23° 28'. Much of the heat must, there- 

 fore, be absorbed by the air, as happens near the hours of sunrise and sunset in our 

 climate. Also " the vast beds of snow and fields of ice, which cover the land, and 

 the sea in those dreary regions, absorb in the act of thawing or passing to the 

 liquid form, all the surplus heat collected during the continuance of a nightless 

 summer. But the rigor of winter, when darkness resumes her tedious reign, is 

 likewise mitigated by the warmth evolved as congelation spreads over the watery 

 surface." (Encyc. Brit., article Climate.) 



The sun's intensity may yet have a somewhat greater effect upon the pole, where 

 it pierces a thinner stratum of the atmosphere than over another portion of the 

 earth's surface. For, in consequence of the centrifugal force of the earth's diurnal 

 motion, the particles of air in all other parts of the earth, being thrown outwards, 

 tend to an increased thickness, in spheroidal strata. We might thence infer that 

 a less proportion of the sun's rays would be absorbed, and a greater portion trans^ 

 mitted through the atmosphere, to the surface of the earth. However this may be 

 in the immediate vicinity of the Pole, yet in the high latitudes hitherto visited by 

 navigators, and which are not nearer than about five or six hundred miles from the 

 North Pole, according to Dr. Kane and others, 1 a dense and lasting fog prevails 

 after the middle of June, through the rest of the summer season, and effectually 

 prevents the rise of temperature which the sun's intensity would otherwise produce. 



The question of an open, unfrozen sea in the vicinity of the North Pole, has not 

 yet been definitely settled. In this connection we shall only glance at some of the 

 evidences on both sides, without discussing further a subject still unreclaimed from 

 the domain of uncertainty. 



"Of this I conceive we may be assured," says Scoresby, Vol. I, p. 46, "that the 

 opinion of an open sea around the Pole is altogether chimerical. We must allow, 

 indeed, that when the atmosphere is free from clouds, the influence of the sun, 

 notwithstanding its obliquity, is, on the surface of the. earth or sea, about the time 

 of the summer solstice, greater at the Pole by nearly one-fourth part, than at the 

 equator. 2 Hence it is urged that this extraordinary power of the sun destroys all the 

 ice generated in the winter season, and renders the temperature of the Pole warmer 

 and more congenial to the feelings than it is in some places lying near the equator. 

 Now, it must be allowed, from the same principle, that the influence in the parallel 

 of 78°, where it is computed in the same way to be only about one forty-fifth part 



1 "The general obscurity of the atmosphere arising from clouds or fogs is such, that the sun is fre- 

 quently invisible during several successive days. At such times, when the sun is near the northern 

 tropic, there is scarcely any sensible quantity of light from noon to midnight." (Scoresby's Arctic 

 Regions, Vol. I, p. 378.) 



" The hoar-frost settles profusely in fantastic clusters on every prominence. The whole surface of the 

 sea steams like a lime-kiln, an appearance called the frost smoke, caused, as in other instances of the 

 production of vapors, by the waters being still relatively warmer than the incumbent air. At length 

 the dispersion of the mist, and the consequent clearness of the atmosphere announce that the upper 

 stratum of the sea itself has become cooled to the same standard; a sheet of ice quickly spreads, and 

 often gains the thickness of an inch in a single night." 



3 See Section IV (IT). The value was first determined by Halley, Phil. Trans., 1693. 



