458 ON THE SOURCES OF HEAT WHICH INFLUENCE CLIMATE. 



since it is established, beyond the possibility of a doubt, that the heat of the 

 central matter of the earth, or the cold that pervades the regions through which 

 our globe revolves, would be alike destructive to the existing organization. 



The variations of the atmosphere, and its temperature from day to day, form of 

 themselves subjects of almost universal interest. In all ages and nations they 

 furnish a never-ending topic for those who wish to exchange a few words in 

 conversation with strangers or passing friends. And we have very recently seen 

 how, in this advanced age, a few fortunate predictions as to the cold of winter 

 have called forward the public most liberally to patronise their author. 



Meteorological changes are powerfully influenced by whatever governs the tem- 

 perature of the atmosphere. The influence of the solar rays at once presents to us 

 a most active agent; yet it will be seen that the sources of heat which must greatly 

 control such fluctuations, are not in the present state of our knowledge easily 

 determined in value. They appear as yet quite unassignable to any precise law. 

 To be well forewarned of the general character of approaching seasons would be of 

 the utmost importance in a domestic point of view ; for this purpose many general 

 rules have been given that are not without their value, though to all of them the 

 exceptions are numerous. Thus an abundant crop of fruit on the plants indigenous 

 to our island, and which grow without any cultivation, is said to precede a severe 

 winter, as for instance the fruit of the Common Hawthorn. Such a belief has 

 been long entertained. Admitting it to be well founded, it only presents to us 

 another beautiful proof of the careful provisions of Nature, as it is during a pro- 

 tracted winter that the spontaneous productions of the wild plants will be most 

 wanted to maintain the numerous classes of wild animals dependent on the food 

 they can procure by their daily search. 



Careful attention to the winds at the vernal equinox, noting the date of their 

 occurrence, their direction and their force, are by some believed to afford data for 

 predicting whether we shall have a wet, a cold, a dry, or a warm summer. In 

 Dr. Rees' Encyclopaedia a table of Dr. Kerwin's is given, by which you may 

 foretell without erring oftener than one in three. 



The height of the line of perpetual snow, above the level of the sea, is by much 

 the most easily-fixed standard for judging of the power of the sun's rays under 

 different latitudes. This for the northern hemisphere is well ascertained ; but 

 for the equinoctial and southern latitudes we require further data before it can be 

 accurately traced. At a short distance from the North Pole the line of perpetual 

 frost leaves the earth, and ascends till it reaches two or three degrees south of the 

 northern tropic. The ascent was long believed to continue onwards until under 

 the equator. More recent inquirers do not admit this, since they can shew that 

 for two months the solar rays fall as perpendicularly at noon on countries lying 

 between 20 and 23^ latitude, as they do on places directly under the equator, for 



