14 Biogi'aphical Accmmt of Dr Wilson, 



ing certain striking alterations of the form both of the nucleus 

 and umbra, that the suggestion first arose in his mind of the 

 spot being an excavation or depression on the luminous matter 

 of the sun ; which idea, the subsequent observations of the same 

 spot most evidently confirmed. 



Not long before his death, in turning over at more leisure 

 the pages of this admirable astronomer, Dr Wilson for the first 

 time met with the above passage, and was pleased at finding so 

 remarkable a coincidence as to the leading fact upon which his 

 discovery rests. 



Among his papers there were found many letters he had re- 

 ceived from Dr Maskelyne, upon whose correspondence Dr 

 Wilson set a very high value. All his papers published in the 

 Philosophical Transactions of London were communicated by 

 that friend. Among these, we find a short one in the volume 

 for 1774, wherein he proposes to diminish the diameter of the 

 finest wires, used in the focus of the astronomical telescope, by 

 flattening them according to a method there described ; an idea 

 which, though very simple, seems extremely worthy of atten- 

 tion. 



In the month of January 1777, when conversing, as he often 

 did in the evenings, with his son, who had now made some pro- 

 ficiency in the sciences, their attention was somehow turned to 

 the following query, proposed by Sir Isaac Newton, among 

 many others, at the end of his optics, namely, " What hinders 

 the fixed stars from failing upon one another P''^ 



In reflecting upon this matter, they readily came to be of 

 opinion, that if a similar question had been put in respect of 

 the component parts of the solar system, it would have admit- 

 ted of a very easy solution, on 2iccour)to^ periodical motiofi ap- 

 pearing to them as the great mean employed by nature for 

 counteracting the power of gravity, and for maintaining the 

 sun and the whole retinue of planets, primary as well as secon- 

 dary, and of comets, at commodious distances from one ano- 

 ther. 



In like manner, Dr Wilson thought it not unreasonable to 

 suppose, that the same principle might have assigned to it a do- 

 minion incomparably wider in extent, and that the order and 

 stability, even of a universe, and of every individual system 



