INFLUENCE OF TEMPERATURE. 9 



live insignificance, so soon as the causes which have forced them from obscurity cease, 

 but of that other class, of whom God makes but one in a century, and gives him a 

 power of enchantment over his fellows, so that by a word, or even by a look, he can 

 " electrify, and guide, and govern mankind." 



27. It was a beautiful idea of some of the English chemists of the seventeenth cen- 

 tury, that our earth is nothing more than an incrusted star a star, the light of which 

 has gone out. They gathered this from the well-known phenomena of hot springs, 

 and the increasing temperature of deep cavities. In their opinion, there was a sun in 

 the earth beneath, as well as a sun in the firmament above. These views are essen- 

 tially the same as those which are now received by geologists, who almost universally 

 admit the doctrine of a central heat, the surface having cooled down nearly to a con- 

 dition of equilibrium. Equally beautiful is the idea of M. POISSON, that the sun, in his 

 movements through space, successively carries his attendant planets through regions of 

 variable temperatures temperatures which are variable by reason of the different amount 

 of stellar radiation which crosses them, and that, for many ages past, he has been com- 

 ing from a warmer to a colder space. Admitting this to be a true representation of the 

 fact, the phenomena which we witness are such as should take place. If a great mass 

 of rock was brought from the equator suddenly into the polar regions, it would, from 

 being exposed there to a low temperature, commence to radiate its heat, and in a very 

 short time, if examined, would be found coldest on the surface, with a temperature in- 

 creasing towards its centre, that increase being at first rapid, but the heat subsequently 

 becoming uniform. Such a rock POISSON regards as being a miniature representation 

 of the earth. 



28. Which ever of these hypotheses is true, of one thing we are certain, that the sur- 

 face temperature of the globe has undergone periodic changes, and with these chan- 

 ges, not only has the distribution of plants and animals varied, but general disturbances 

 have taken place in the types of existing species. Those creations and extinctions to 

 which allusion has been made were all, undoubtedly, connected with these thermal dis- 

 turbances. There can be little doubt that the mastodontoid family was destroyed by a 

 general reduction of temperature. With modifications of the distribution of this all- 

 pervading agent, changes in the distribution of organized beings must of necessity ensue. 

 Even with us, were the mean temperature to rise by a few degrees, the great mamma- 

 lia of the torrid zone would push their excursions to the north and south. The Ben- 

 gal tiger would leave his jungle, and press himself into higher latitudes. It would re- 

 quire but a slight meteorological change to bring the orange-tree into the Middle States, 

 or to tempt the turkey-buzzard far to. the north of New- York. And, on the other 

 hand, should a reverse action take place, and the mean temperature descend by a few 

 degrees, the indigenous animals and plants of the Northern States must pass to a lower 

 latitude, or become extinct. The distribution of organized forms is, therefore, directly, 

 and their very existence indirectly, determined by the distribution of heat. Who, then, 

 can doubt that all living beings depend on physical force? 



29. If these things are true with respect to the organized forms which are known 

 to have existed in former times and we examine the relations obtaining between the 



B 



