xviii.] OBSERVATION. 403 



one of the forces of the problem, and the true course of 

 external nature might still be rendered apparent. But the 

 feelings of an observer are usually too indeterminate, so 

 that when there is reason to suspect considerable bias, re- 

 jection is the only safe course. As regards facts casually 

 registered in past times, the capacity and impartiality of 

 the observer are so little known that we should spare no 

 pains to replace these statements by a new appeal to 

 nature. An indiscriminate medley of truth and absurdity, 

 such as Francis Bacon collected in his Natural History, is 

 wholly unsuited to the purposes of science. But of course 

 when records relate to past events like eclipses, con- 

 junctions, meteoric phenomena, earthquakes, volcanic 

 eruptions, changes of sea margins, the existence of now 

 extinct animals, the migrations of tribes, remarkable 

 customs, &c., we must make use of statements however 

 unsatisfactory, and must endeavour to verifiy them by the 

 comparison of independent records or traditions. 



When extensive series of observations have to be made, 

 as in astronomical, meteorological, or magnetical observa- 

 tories, trigonometrical surveys, and extensive chemical or 

 physical researches, it is an advantage that the numerical 

 work should be executed by assistants who are not interested 

 in, and are perhaps unaware of, the expected results. The 

 record is thus rendered perfectly impartial. It may even 

 be desirable that those who perform the purely routine 

 work of measurement and computation should be un- 

 acquainted with the principles of the subject. The great 

 table of logarithms of the French Revolutionary Govern- 

 ment was worked out by a staff of sixty or eighty 

 computers, most of whom were acquainted only with the 

 rules of arithmetic, and worked under the direction of 

 skilled mathematicians; yet their calculations were usually 

 found more correct than those of persons more deeply 

 versed in mathematics. 1 In the Indian Ordnance Survey 

 the actual measurers were selected so that they should 

 not have sufficient skill to falsify their results without 

 detection. 



Both passive observation and experimentation must, 

 however, be generally conducted by persons who know for 



1 Babbage, Economy of Manufactures, p. 194. 



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