OBSERVATION. 



assistants can supersede the mind-directed observations 

 of the philosopher. Thus the successful investigator must 

 combine diverse qualities ; he must have clear notions 

 of the result he expects, and confidence in the truth of his 

 theories, and yet he must have that candour and flexi- 

 bility of mind, which enable him to accept unfavourable 

 results and abandon mistaken views. 



Instrumental and Sensual Conditions of Correct 

 Observation. 



In every observation one or more of the senses must be 

 employed, and we should ever bear in mind that the ex- 

 tent of our knowledge may be limited by the power of the 

 sense concerned. What we learn of the world only forms 

 the lower limit of what is to be learned, and, for all that 

 we can tell, the processes of nature may indefinitely sur- 

 pass in variety and complexity those which are capable of 

 coming within our means of observation. In some cases 

 inference from observed phenomena may make us in- 

 directly aware of what cannot be directly felt, but we 

 can never be sure that we thus acquire any appreciable 

 fraction of the knowledge that might be acquired. 



It is a strange reflection that space may be filled with 

 dark wandering stars, whose existence could not have yet 

 become in any way known to us. The planets have 

 already cooled so far as to be no longer luminous, and it 

 may well be that other stellar bodies of various size have 

 fallen into the same condition. From the consideration, 

 indeed, of variable and extinguished stars, Laplace inferred 

 that there probably exist opaque bodies as great and 

 perhaps as numerous as those we see 6 . Some of these 

 dark stars might ultimately become known to us, either by 

 reflecting light, or more probably by their gravitating 



e 'System of the World,' translated by Harte, vol. ii. p. 335. 



