SCIENTIFIC PREDICTION 195 



close search could not have failed to make the planet 

 known. 



Both Adams and Leverrier had assumed as a 

 rough approximation at starting that the orbit of the 

 new planet was circular and that, in accordance with 

 Bode's Law, its distance was twice that of Uranus. 

 S. C. Walker, of the Smithsonian Institution, Wash- 

 ington, was able to determine the elements of the 

 orbit of Neptune accurately in 1847. In February 

 of that year he had found (as had Petersen of Al- 

 tona about the same time) that Lalande had in May, 

 1795, observed Neptune and mistaken it for a fixed 

 star. When Lalande's records in Paris were studied, 

 it was found that he had made two observations of 

 Neptune on May 8 and 10. Their failure to agree 

 caused the observer to reject one and mark the other 

 as doubtful. Had he repeated the observation, he 

 might have noted that the star moved, and was hi 

 reality a planet. 



Neptune's orbit is more nearly circular than that 

 of any of the major planets except Venus. Its dis- 

 tance is thirty times that of the earth from the sun 

 instead of thirty-nine times, as Bode's Law would 

 require. That generalization was a presupposition 

 of the calculations leading to the discovery. It was 

 then rejected like a discredited ladder. Man's con- 

 ception of the universe is widened at the thought 

 that the outmost known planet of our solar system 

 is about 2,796,000,000 miles from the sun and 

 requires about 165 years for one revolution. 



Professor Peirce, of Harvard University, point- 

 ing to the difference between the calculations of 

 Leverrier and the facts, put forward the view that 



