INTRODUCTION. 6 



The first considers the structure and growth of the earth ; the 

 second, its features and world-wide activities in its finished state ; 

 the third, the fulfilment of its purpose in man, for whose pupil- 

 age it was made. 



5. Relation of the earth to the universe. — While recognizing the 

 earth as a sphere in a world-kingdom, it is also important to observe 

 that the earth holds a very subordinate position in the system of 

 the heavens. It is one of the smaller satellites of the sun, — its size 

 about l-1400,000th that of the sun. And the planetary system to 

 which it belongs, although 3,000,000,000 of miles in radius, is but 

 one among myriads, the nearest star 7000 times farther off than 

 Neptune. Thus it appears that the earth is a very little object in 

 the universe. Hence we naturally conclude that the earth is but 

 a dependent part of the solar system ; that as a satellite of the 

 sun, in conjunction with other planets, it could no more have 

 existed before the sun, or our planetary system before the uni- 

 verse of which it is a part, than the hand before the body which 

 it obediently attends. 



Although thus diminutive, the laws of the earth are the laws of 

 the universe. One of the fundamental laws of matter is gravita- 

 tion ; and this we trace not only through our planetery system, 

 but among the fixed stars, and thus know that one law pervades 

 the universe. 



The rays of light which come in from the remote limits of space 

 are a visible declaration of unity ; for this light depends on mole- 

 cular vibrations, — that is, the ultimate constitution and mode of 

 action of matter ; and by the identity of its principles or laws, 

 whatever its source, it proves the essential identity of the molecules 

 of matter. 



Meteoric stones are specimens of celestial bodies occasionally 

 sent to us from the heavens. They exemplify the same chemical 

 and crystallographic laws as the rocks of the earth, and have 

 afforded no new element or principle of any kind. 



The moon presents to the telescope a surface covered with the 

 craters of volcanoes, having forms that are well illustrated by some 

 of the earth's volcanoes, although of immense size. The principles 

 exemplified on the earth are but repeated in her satellite. 



6. Thus, from gravitation, light, meteorites, and the earth's satel- 

 lite, we learn that there is oneness of law through space. The 

 elements may differ in different systems, but it is a difference such 

 as exists among known elements, and could give us no new funda- 

 mental laws. New crystalline forms might be found in the depths 

 of space, but the laws of crystallography would be the same that 



