8i2 THE POPULAR SCIENCE MONTHLY. 



movements, and by its loss or gain of heat. Every mountain, 

 however lofty, is being thrown down ; every rock, however hard, 

 is being worn away ; and every sea, however deep, is being filled 

 up. The destructive agencies of nature are in never-ceasing ac- 

 tivity ; the erosive and dissolving power of water in its various 

 forms, the disintegrating forces of heat and cold, the chemical 

 modification of substances, the mechanical effects produced by 

 winds and other agencies, the operation of vegetable and animal 

 organisms, and the arts and contrivances of man, combine in the 

 warfare against what is. But hand in hand with this destruc- 

 tion — nay, as a part of it — there is everywhere to be found corre- 

 sponding reconstruction, for untiring nature immediately builds 

 up again that which it has just thrown down. If continents are 

 disappearing in one direction, they are rising into fresh existence 

 in another. Though the ocean tears down the cliffs against which 

 it beats, the earth takes its revenge by upheaving the ocean's bed. 

 When we look back, by the help of geological science, to the 

 more remote past, through the epochs preceding our own, we find 

 complete evidence that the globe has passed in succession through 

 an infinitude of anterior states, by means of small modifications 

 extending over a vast period of time, but not differing in essen- 

 tials from those which we now see to be going on. There are still 

 preserved to us the remains of land and marine plants and ani- 

 mals — which lived, produced other generations, and died — pos- 

 sessed of organs proving that they were under the influence of 

 the heat and light of the sun ; indications of seas whose waves 

 rose before the winds, breaking down cliffs, and forming beaches 

 of bowlders and pebbles ; of tides and currents spreading out 

 banks of sand and mud, on which are left the impress of the rip- 

 ple of the water, of drops of rain, and of the tracks of animals; 

 of volcanoes pouring forth streams of lava ; and all these appear- 

 ances are precisely similar to those we observe at the present day 

 as the result of forces which we see actually in operation. Push- 

 ing back our inquiries, we at last reach the point where the 

 apparent cessation, or failure of evidence, of former terrestrial 

 conditions such as now exist, requires us to consider the relation 

 in which our jjlanet stands to other bodies in celestial space ; and, 

 vast though the gulf be that separates us from these, science has 

 been able to bridge it. By means of spectroscopic analysis, it has 

 been established that the constituent elements of the sun and 

 other heavenly bodies are substantially the same as those of the 

 earth. The examination of the meteorites which have fallen on 

 the earth from the interplanetary spaces, shows that they contain 

 nothing foreign to the constituents of the earth. The inference 

 seems legitimate, corroborated as it is by the manifest physical 

 connection between the sun and the planetary bodies circulating 



