THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Art. XI. — On the Observation of Sudden Phenomena • by 

 S. P. Langley. 



[Read before the Philosophical Society of Washington, March 2, 1889.] 



By a sudden phenomenon is here meant one of that large 

 class where the occurrence is awaited without the observer's 

 previous knowledge of its exact instant, and of which familiar 

 examples may be found in the bursting of a rocket, the ap- 

 pearance of a meteor, or the emergence of a star from behind 

 the moon. A great part of all the phenomena of daily life, 

 as well as of scientific observation, are of this kind, though 

 the importance of a special instance of another class, (I refer 

 to the gradual and foreseen approach of a star to a wire), has 

 drawn to this latter such particular attention that we are 

 apt to think of it only when u personal error " is in question. 



When in an observatory, we study the means taken to 

 record the precise time of the transit of a star, we find that 

 the precision of modern apparatus has reduced the error 

 which we may expect in almost any part of the mechanism to 

 an extremely minute amount, which may be calculated to the 

 fractional part of the one hundredth of a second. I say 

 " almost " for, as we are all aware, there is one notable excep- 

 tion, at least until photography can be made to intervene. The 

 human brain and nerves, and behind these the inscrutable pro- 

 cesses of the will, themselves form an inevitable link in the 

 chain of apparatus of observation, and here an error may and 



Am. Jour. Sci.— Third Series, Vol. XXXVIII, No. 224.— August, 1889. 

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