T H E 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUKNAL OF SCIENCE. 



[FIFTH SERIES.] 



JUL Y 1877, 



I. On Fallible Measures of Variable Quantities^ and on the T'reat" 

 ment of Meteorological Observations. By Gc. H. Darwin, 

 M.A., Fellow of IVlnity College ^ Cambridge* . 



IF we iQake any observation, for example the transit of a 

 star, a definite numerical result is obtained. To say that 

 that result is liable to errors of observation, is only correct 

 from one point of view. It is true that the result does not 

 really correspond with the time at which the star crossed the 

 meridian, yet it is an accurate representation of a certain very 

 complex event. Undoubtedly, the principal feature in that 

 event is the time of crossing the meridian ; but there is also 

 involved in it various properties of the instruments, the atmo- 

 sphere, and the observer himself, &c. The object of the obser- 

 vation is, of course, to get a result which shall represent that 

 principal feature, after the elimination of the minor features. 

 The comparative simplicity of this, and of many other obser- 

 vations, permits us to unravel the complex event into its con- 

 stituent parts, and to estimate each numerically. One part 

 consists of corrections of all sorts. But when all these have 

 been made, there still remains a result representing a complex 

 event, viz. the transit of the star, together with unknown 

 properties of the circumstances of the observation. These 

 unknown properties form the subject-matter of the theory of 

 errors of observation ; but it is only because there is a consistent 

 theory of the principal phenomenon, that the most probable 

 line of demarcation can be drawn between the two parts of 

 the complex event. The final result is given as a definite 

 value with a margin of uncertainty in either direction. 



But in the case of astronomical observations there is com- 

 * Communicated by the Author. 



FhiL Mag. S. 5. Yol. 4. No. 22. July 1877. B 



