Conditions of Life, 49 



of the agencies that secure the result. How futile 

 would be the keenest Instinct of animals, and how 

 useless all the machinery in the vegetable kingdom 

 for the distribution of plants, if the earth itself were 

 not a preserver of both animals and plants by the 

 balance of its forces and the ready yielding of its 

 elements for their protection and support ! 



We cannot tell what compensations there may 

 be on other planets to make such life as our earth has 

 possible on them, or what forms of life may be fitted 

 to flourish under their physical conditions ; but the 

 constitution of our earth we can understand, and 

 the capabilities of all living forms both of plants 

 and animals we are able to gauge. If we cannot 

 mark the exact power of endurance of each kind, 

 we can set a limit of cold and heat beyond which 

 no living thing could exist. A nearness to the sun 

 that should give us a temperature of three hundred 

 degrees in every portion of the globe would render 

 the existence of every known form of life now upon 

 our earth impossible. A temperature of zero con- 

 tinued for ages would bring all oceans to solid ice, 

 and in the end make the earth a barren waste. 



Let the earth then wander from her path and 

 approach the sun until she circles far within the or- 

 bit of Mercury, or let her forget the centripetal 

 force and extend her path to the outer verge of the 

 solar system ; in one case she would become a blaz- 

 ing ball until wrapped in the terrible mantle of 

 oceans changed to steam ; in the other, earth and 

 water would be changed to solid stone and the sum- 

 mer's cold would exceed the deadly breath of arctic 



