86 



INHERITANCE IN ANIMALS 



Determinations of the Latitude of the Raddiffe Transit Circle. 

 Year. Latitude. Year. Latitude. 



1840 5i45'35"85 1865 5i45'35"-28 



You see that up to a certain point, all the experience 

 of this angle, acquired and recorded by highly trained 

 observers during nearly half a century, is constant. The 

 latitude is always greater than 5i45', and nearly always 

 greater than 5i45'35"; but when these men try to record 

 observations of less than a second, their successive records 

 do not agree. The difference between the highest and 

 the lowest values of the latitude observed is i"-O2, which 

 corresponds to a distance of about thirty-four yards 

 measured on the Earth's surface, North and South 

 through the telescope ; and the remaining values are 

 scattered between these limits. 



Now although thirty-four yards is a very sensible 

 distance, considered in itself, it is a very small fraction 

 of the distance on the Earth's surface from the Radcliffe 

 telescope to the Equator. A line drawn due south from 

 that telescope to the Equator would be about 6,300,000 

 yards long, so that the extreme range over which un- 

 certainty about the result of any one measurement has 

 been shown to extend is less than one part in 180,000 of 

 the whole magnitude measured. This may be taken as 

 a type of a very excellent experimental approximation to 

 a constant result. We can predict the result which any 

 properly trained person will get, if he measures this angle 

 of latitude again, to within a very small fraction of the 



