312 * Of the Propagation of Heat 



Let me beg the attention of my reader while I endeav- 

 our to investigate this most interesting subject, and let 

 me at the same time bespeak his candour and indulgence. 

 I feel the danger to which a mortal exposes himself who 

 has the temerity to undertake to explain the designs of 

 Infinite Wisdom. The enterprise is adventurous, but 

 it cannot surely be improper. 



The wonderful simplicity of the means employed by 

 the Creator of the world to produce the changes of the 

 seasons, with all the innumerable advantages to the inhab- 

 itants of the earth which flow from them, cannot fail to 

 make a very deep and a lasting impression on every human 

 being whose mind is not degraded, and quite callous to 

 every ingenuous and noble sentiment ; but the farther 

 we pursue our inquiries respecting the constitution of 

 the universe, and the more attentively we examine the 

 effects produced by the various modifications of the ac- 

 tive powers which we perceive, the more we shall be dis- 

 posed to admire, adore, and love that great First Cause 

 which brought all things into existence. 



Though winter and summer, spring and autumn, and 

 all the variety of the seasons, are produced in a manner 

 at the same time the most simple and the most stupen- 

 dous (by the inclination of the axis of the earth to the 

 plane of the ecliptic), yet this mechanical contrivance 

 alone would not have been sufficient (as I shall endeavour 

 to show) to produce that gradual change of temperature in 

 the various climates which we find to exist, and which 

 doubtless Is indispensably necessary to the preservation 

 of animal and vegetable life. 



Though change of temperature seems necessary to the 

 growth and perfection of most vegetables, yet these 

 changes must be within certain limits. Some plants can 



