32 ENLARGED YIEWS OF PHYSICAL 



in seeming contradiction with each other. Such is the kind 

 of expectation at present excited by meteorology, by many 

 parts of optics, and, since the admirable labours of Melloni 

 and Faraday, by the study of radiant heat and of electro- 

 magnetism. The circle of brilliant discoveries has here still 

 to be run through ; although the Yoltaic pile already reveals 

 the wondrous connection of electrical, magnetical, and che- 

 mical phenomena. Who will venture to affirm, that we yet 

 know with precision that part of the atmosphere which is 

 not oxygen, or that thousands of gaseous substances affect- 

 ing our organs may not be mixed with the nitrogen ? or 

 who will say that we already know even the whole number 

 of the forces which prevade the universe ? 



It is not the purpose of this work to attempt to reduce 

 all sensible phsenomena to a small number of abstract prin- 

 ciples, having their foundation in pure reason only. The 

 physical cosmography of which I attempt the exposition 

 does not aspire to the perilous elevation of a pure rational 

 science of nature. Leaving to' others, who may perhaps 

 adventure on them with more success, these depths of a 

 purely speculative philosophy, my essay on the Cosmos con- 

 sists of physical geography, joined with the description 

 of the heavenly bodies in space : its aim is to present 

 a view of the material universe, which may rest on the 

 experimental foundation of the facts registered by science, 

 compared and combined by the operations of the intel- 

 lect. It is within these limits alone that the under- 

 taking can harmonise with the wholly objective tendency of 

 my mental disposition, and with the labours which have 

 occupied my long scientific career. The unity which I seek 

 to attain in the development of the great phenomena of 



