llEtEOROLOGY 13 



island has in winter been reduced 20^ to 30^, there exists a strong 

 tendency to the restoration of equilibruin with the wanner atmosphere 

 of the contiguous ocean. The first effects of condensation then, in the 

 contact of strata of air of differing density and temperature containing 

 aqueous vapour ensues, and we soon perceive indications of change, 

 by tlie formation of cirrus, the lightest modification of cloud in the higher 

 regions of the air; the sky speedily becomes obscured, heat which 

 before was radiated from the earth and dissipated, is now prevented 

 from escaping by opaque clouds, and a gradual rise of temperature is 

 the result, geneially followed by rain : we thus see that it arises from 

 the insular position of this country that the weather is subject to such 

 frequent changes in winter. The alternate action of radiation from 

 the earth, and reflection by the clouds, is often very sensibly evinced 

 during seasons of severe cold ; a passing cloud will occasion a rise in 

 the thennometer of a degree or more, the radiated heat being confined 

 by the cloud near the earth ; when the cloud has passed and the sky 

 has vertically become clear, the thennometer again falls, the radiation 

 being uninterrupted and the heat lost in space. 



The same principles are effective over the earth's entire surface, each 

 prevailing in proportion to the predominance of large surfaces of earth 

 or ocean. Within the tropics the vertical rays of the sun are so 

 absorbed in continental situations as to occasion intense heat, in islands 

 and places on the coast nearer to the ocean the heat is mitigated : again, 

 within the arctic circle, the heat absorbed during the brief summer is 

 rapidly radiated when the sun approaches the horizon, and during his 

 long absence the earth's surface is at its lowest temperature. It is 

 well known that the atmosphere of the sea coast in this country is 

 cooler during the summer months than the interior of the island ; it is 

 equally true, though perhaps less generally known, that in winter the 

 sea coast is warmer than the interior, its annual lange of temperature 

 being more limited and uniform. 



Seeing then that all the elements of weather and its changes aie 

 essentially dependent on temperature and its variations, it is proper 

 to enquire whether the moon, planets or stars have been ascertained 

 to produce thermal action on the earth's surface. That the planets, in 

 common with the fixed stars, are powerless in exciting heat, may be 

 regarded as certain by the following fact — their combined effect in 

 those parts of the globe refrigerated by the long absence of the sim. 



