INTRODUCTION. 9 



gradual development and extension, have attained a higher 

 degree of advancement, and until we shall have gained a 

 more extended knowledge of the two grand divisions of the 

 Cosmos — the external world, as made perceptible to us by 

 the senses ; and the inner, reflected intellectual world. 



I think I have here sufficiently indicated the reasons which 

 determined me not to give greater 6xtension to the general 

 picture of nature. It remains for this third and fourth volume 

 of my Cosmos to supply much that is wanting in the previ- 

 ous portions of the work, and to present those results of ob- 

 servation on which the present condition of scientific opinion 

 is especially grounded. I shall here follow a similar mode 

 of arrangement to that previously adopted, for the reasons 

 which I have advanced, in the delineation of nature. But, 

 before entering upon the individual facts on which special 

 departments of science are based, I would fain offer a few 

 more general explanatory observations. The unexpected in- 

 dulgence with which my undertaking has been received by 

 a large portion of the public, both at home and abroad, ren- 

 ders it doubly imperative that I should once more define, as 

 distinctly as possible, the fundamental ideas on which the 

 whole work is based, and say something in regard to those 

 demands winch I have not even attempted to satisfy, be- 

 cause, according to my view of empirical — i. e., experiment- 

 al — science, they did not admit of being satisfied. These 

 explanatory observations involuntarily associate themselves 

 with historical recollections of the earlier attempts made to 

 discover the one universal idea to which all phenomena, in 

 their causal connection, might be reduced, as to a sole prin- 

 ciple. 



The fundamental principle* of my work on the Cosmos, 

 as enunciated by me more than twenty years ago, in the 

 French and German lectures I gave at Paris and Berlin, 

 comprehended the endeavor to combine all cosmic al phenom- 

 ena in one sole picture of nature ; to show in what manner 

 the common conditions, that is to say, the great laws, by 

 which individual groups of these phenomena are governed, 

 have been recognized ; and what course has been pursued 

 in ascending from these laws to the discovery of their causal 

 connection. Such an attempt to comprehend the plan of 

 the universe — the order of nature — must begin with a gen- 

 eralization of particular facts, and a knowledge of the con* 



# Cosmos, vol. i., p. 48-50, and 68-77. 



