388 ACTUAL WORKING IN ORIGINAL RESEARCH. 



measurement and patient, long-continued labour in the 

 minute sifting of numerical results. The popular idea of 

 Newton's grand discovery is, that the theory of gravita- 

 tion flashed upon his mind, and so the discovery was 

 made. It was by a long train of mathematical calcula- 

 tion, founded on results accumulated through prodigious 

 toil of practical astronomers, that Newton first demon- 

 strated the forces urging the planets towards the sun, 

 determined the magnitude of those forces, and discovered 

 that a force following the same law of variation with 

 distance urges the moon towards the earth. Then, first, 

 we may suppose, came to him the idea of the universality 

 of gravitation ; but when he attempted to compare the 

 magnitude of the earth's surface, he did not find the 

 agreement which the law he was discovering required. 

 Not for years after would he publish his discovery as 

 made. It is recounted that, being present at a meeting 

 of the Royal Society, he heard a paper read, describing 

 geodesic measurement by Picard, which led to serious 

 correction of the previously accepted estimate of the earth's 

 radius. This was what Newton wanted. He went home 

 with the result, and commenced his calculations, but felt 

 so agitated that he handed over the arithmetical work to 

 a friend ; then (and not when, sitting in a garden, he saw 

 an apple fall) did he ascertain that gravitation keeps the 

 moon in her orbit. Faraday's discovery of specific in- 

 ductive capacity which inaugurated the new philosophy, 

 tending to discard action at a distance, was the result 

 of minute and accurate measurement of electric forces. 

 Joule's discovery of thermo-dynamic law, through the 

 regions of electro-chemistry, electro-magnetism, and elas- 

 ticity of gases, was based on a delicacy of thermometry 

 which seemed impossible to some of the most distinguished 

 chemists of the day. Andrew's discovery of the continuity 



