METEOROLOGY. 321 



ON THE RELATIVE INTENSITY OF THE HEAT AND LIGHT 

 OF THE SUN UPON DIFFERENT LATITUDES OF THE 

 EARTH. 



BY L. W. MEECH. 



The ninth volume of the Smithsonian Contributions to Knowledge 

 contains a memoir, which, under the above title, presents the astro- 

 nomical determinations of the relative number of heating and illu- 

 minating rays received from the sun upon any portion of the exterior 

 surface of the earth. During their passage through the air in im- 

 pinging upon the solid earth, the rays are modified by a variety of 

 circumstances ; still the primary intensity of the sun is the controlling 

 cause of the changes of temperature of the seasons, and therefore the 

 determination of its laws has a special importance. 



The subjoined account, with slight additions, contains nearly all of 

 the paper referred to, except the mathematical portions, for which, 

 reference may be made whenever necessary to the original memoir. 



The regular and almost uniform variations which meteorological 

 tables exhibit, indicate a periodical cause of change, which evidently 

 resides in the sun. The inquiry then arises, may not these variations 

 be determined by theory from the apparent course of the sun ? 



The object of the investigation here presented is to resolve the pro- 

 blem of solar heat and light, to the extent of the principle, that the 

 intensity of the sun's rays, like gravitation, varies inversely as the 

 square of the distance, without resorting to any other hypothesis. 

 The principle is but a geometrical consequence of the divergence of the 

 rays. This elementary view thus presents the sun shining upon a 

 distant planet, and indicates the sum of the intensities received at the 

 planet's surface in all its various phases of position and inclination. 



In relation to the earth especially, the sum of the intensities must 

 be referred to the exterior limit of the atmosphere which surrounds 

 the globe. This condition, which is perhaps necessary in the present 

 state of science, has the advantage of rendering the deductions as 

 rigorously accurate as are the propositions of geometry and the conic 

 sections. 



Poisson, in 1835, observed that, "for the completion of the theory 

 of heat, it is necessary that it should comprise the determination of 

 the movements produced in aeriform fluids, in liquids and even in 

 sojid bodies; but geometers have not yet resolved this order of ques- 

 tions, of great difficulty, with which are connected the phenomena of 



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