X PREFACE. 



Discoveries, when once communicated to the world, 

 become public property : they are thrown into the 

 common stock for mutual benefit ; and it is only in the 

 case of debateable opinions, or of any recent and un- 

 confirmed observations, that it really interests the world 

 that authorities should be quoted at all. In the lan- 

 guage of a highly valued friend, when writing upon 

 another subject : " The advanced state of a science is 

 but the accumulation of the discoveries and inventions 

 of many : to refer each of these to its author is the 

 business of the history of science, but does not belong 

 to a work which professes merely to give an account of 

 the science as it is : all that is generally acknowledged 

 must pass current from author to author." * 



* Brett's Principles of Astronomy, p. v. 



LONDON, 



June, 1848. 



