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THE POPULAR SCIENCE MONTHLY 



by Prof. Leconte that there are no 

 less than three hundred and seveuty 

 facts concerning the distribution, form, 

 and motions, of the sun and planets, 

 which are the simple consequences of 

 the nebular hypothesis, and can be ac- 

 counted for in no other way. The 

 nebular hypothesis is the doctrine of 

 to-day, in its application to tbe most 

 perfect of the sciences, and it is nothing 

 less or other than an hypothesis of as- 

 tronomic evolution. Are we to be told 

 that it is but an a 'priori speculation? 

 On the contrary, has it not replaced an 

 a priori cosmogony that swayed the 

 human mind for thousands of years be- 

 fore the solar system was discovered? 



As regards the earth, it has been 

 studied by the method of science for 

 more than a century, and the result is, 

 a vast mass of facts and inductions 

 which make up our knowledge of geol- 

 ogy. All these go to establish one 

 proposition, viz., that our planet is not 

 what it was millions of years ago, but 

 has undergone a series of developing 

 changes resulting in the present order 

 of things. Our eminent geologist, Prof. 

 Dana, in his manual, says : " This law of 

 specialization the general being before 

 the special is the law of all develop- 

 ment. The egg is at first a simple unit, 

 and, gradually, part after part of the 

 new structure is evolved, that which is 

 most fundamental appearing earliest, 

 until the being is complete in all its 

 outer and minor details. The principle 

 is exhibited in the physical history of 

 the globe which was first a featureless 

 globe of fire, then had its oceans and 

 dry land, in course of time received 

 mountains and rivers, and finally all 

 those diversities of surface which now 

 characterize it. Again, the climates 

 began with universal tropics; and at 

 last the diversities of the present day." 

 Is this to be accounted a high-flown 

 a priori speculation, or a vast and valid 

 induction from a hundred years' study 

 of the facts of Nature ? Let it be re- 

 membered that, according to the high- 



est authorities, inductive geology was 

 put back two centuries by the en- 

 slavement of the human mind to an 

 old a priori speculation in regard to 

 the age of the world. 



The study of the course of life upon 

 the earth shows that it conforms to the 

 same great plan. The life of the globe 

 a few millions of years ago was a very 

 different thing from what it is now. 

 Different races of plants and animals 

 have appeared and disappeared in slow 

 succession, and their remains are found 

 entombed in successive rock-forma- 

 tions. The facts are a part of geology, 

 and have been arrived at by the same 

 processes of observation and induction 

 that have revealed the order and his- 

 tory of the stratified systems. The 

 course of life upon the earth has con- 

 formed to a method, and that method 

 is universally described as a progress 

 and a development. It shows an ad- 

 vance from the simpler to the more 

 complex, from the general to the 

 special, from the lower to the higher; 

 in short, it is an evolution in the strict- 

 est sense. There was, first, a period 

 of no life the azoic age ; then ap- 

 peared the lower forms of life, vegeta- 

 ble and animal ; then higher and higher 

 kinds, until man, the highest of all, ap- 

 peared last. The progress evinces con- 

 tinuity, harmony, and gradation. As 

 remarked by Mr. Dana, "the begin- 

 ning of an age will be in the midst of a 

 preceding age; and the marks of the 

 future coming out to view are to be 

 regarded as prophetic of that future. 

 The age of mammals was foreshadowed 

 by the appearance of mammals long 

 before in the course of the reptilian 

 age, and the age of reptiles was prophe- 

 sied in types that lived in the earlier 

 Carboniferous age." The lower forms 

 that perish do not reappear, and, as Mr. 

 Wallace observes, " no group or species 

 has come into existence twice," but 

 " every species has come into existence 

 coincident, both in space and time, with 

 a preexisting, closely-allied species." 



