II THE PROGRESS OF SCIENCE 63 



some of which, to ordinary apprehension, seem 

 physical antinomies. 



It sounds paradoxical to say that the attainment 

 of scientific truth has been effected, to a great 

 extent, by the help of scientific errors. But the 

 subject-matter of physical science is furnished by 

 observation, which cannot extend beyond the limits 

 of our faculties ; while, even within those limits, 

 we cannot be certain that any observation is ab- 

 solutely exact and exhaustive. Hence it follows 

 that any given generalisation from observation 

 may be true, within the limits of our powers 

 of observation at a given time, and yet turn 

 out to be untrue, when those powers of 

 observation are directly or indirectly enlarged. 

 Or, to put the matter in another way, a doctrine 

 which is untrue absolutely, may, to a very great 

 extent, be susceptible of an interpretation in ac- 

 cordance with the truth. At a certain period in 

 the history of astronomical science, the assumption 

 that the planets move in circles was true enough 

 to serve the purpose of correlating such observa- 

 tions as were then possible ; after Kepler, the 

 assumption that they move in ellipses became 

 true enough in regard to the state of observational 

 astronomy at that time. We say still that the 

 orbits of the planets are ellipses, because, for all 

 ordinary purposes, that is a sufficiently near 

 approximation to the truth ; but, as a matter of 

 fact, the centre of gravity of a planet describes 



