102 HISTORY OF THE PHYSICAL 



of the physical contemplation of the universe/' must not, 

 therefore, be confounded with the " history of the natural 

 sciences/' as it is given in several of our best elementary 

 books of physics, or in those of the morphology of plants 

 and animals. In order to afford some preliminary notion of 

 the import and bearing of what is to be here contemplated 

 as historic periods or epochs, it may be useful to give 

 instances, shewing on the one hand what is to be treated 

 of, and on the other hand what is to be excluded. The 

 discoveries of the compound microscope, of the telescope, 

 and of colored polarisation, belong to the history of the 

 science of the Cosmos, because they have supplied the 

 means of discovering what is common to all organic bodies, 

 of penetrating into the most distant regions of space, and 

 of distinguishing borrowed or reflected light from that of 

 self-luminous bodies, i. e. of determining whether the light 

 of the sun proceeds from a solid mass, or from a gaseous 

 envelope; whilst, on the other hand, the relation of the experi- 

 ments which, from the time of Huygens, have gradually led 

 to Arago's discovery of colored polarisation, is reserved for 

 the history of optics. In like manner the development of the 

 principles according to which the varied mass of vegetable 

 forms may be arranged in families is left to the history of 

 phytognosy or botany ; whilst what relates to the geography 

 of plants, or to the insight into the local and climatic distri- 

 bution of vegetation over the whole globe, on the dry land 

 and in the alga3ferous basin of the sea, constitutes an im- 

 portant section in the history of the physical contemplation 

 of the universe. 



The thoughtful consideration of that which has conducted 

 men to their present degree of insight into nature as a 



