290 Mary Somerville. 



same time, that each country claims the honour of 

 the discovery. Mr. Adams told Somerville that the 

 following sentence in the sixth edition of the " Con- 

 nexion of the Physical Sciences/' published in the year 

 1842, put it into his head to calculate the orbit of 

 Neptune. "If after the lapse of years the tables 

 formed from a combination of numerous observa- 

 tions should be still inadequate to represent the 

 motions of Uranus, the discrepancies may reveal 

 the existence, nay, even the mass and orbit of a 

 body placed for ever beyond the sphere of vision." 

 That prediction was fulfilled in 1846, by the dis- 

 covery of Neptune revolving at the distance of 

 3,000,000,000 of miles from the sun. The mass of 

 Neptune, the size and position of his orbit in space, 

 and his periodic time, were determined from his dis- 

 turbing action on Uranus before the planet itself had 

 been seen. 



We left Collingwood as ever with regret. 



[The following is an extract from a letter written by my 

 mother during this visit : 



FEOM MRS. SOMERVILLE TO W. GREIG, ESQ. 



UOLLINGWOOD, 1st January, 1848. 



.... You can more easily conceive than I can 

 describe the great kindness and affection which we have 

 received from both Sir John and Lady Herschel ; I feel 



