1826.] Biographical Account of Dvi. Wilson, 331: 



word macula, Mr. Flamstead evidently means the nucleus of the 

 spot, and by nubicula the dusky zone which surrounds it. 



*' 1676, Nov. 9. Deinde densi adeo vapores excepere solem, 

 ut per ipsos licuit ilium nudis oculis intueri. Adhibito tum lon- 

 giore tubo absque vitro rubro, (quo oculum ad versus ejus splen- 

 dorem munire soleo) maculum contemplatus sura : distincta 

 vald^ videbatur, ej usque figurae qu38 in schemate adpingitur : 

 ' Nubecula ipsi circumducta ellipiica omnino ; sed, quod vaid^ 

 miratus sum, admodum dilatata a parte limbum respiciente ; ab 

 altera vero versus centrum, maculae fere cohserere videbatur.' 



** Observavi dein maculae a limbo proximo distantium V IS^'V 

 Hist. Calest. Flamsteadii, Yo\, prim. p. 363. 



When Dr. Wilson saw the great spot on the 23d November, 

 1769, it had nearly the same situation upon the disk, and the 

 same aspect as the one here described. But, at that time, like 

 Mr. Flamstead, he had no conception of what was signified by 

 such an appearance. It was not till next day, after remarking 

 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 sp 

 remarkable a coincidence as to the leading fact upon which his 

 discovery rests. 



Among his papers there were found many letters he had 

 received from Dr. Maskelyne, upon whose correspondence Dr. 

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

 the London Philosphical Transactions, 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 th^ 

 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 attention. 



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 falling upon one another ?" 



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 admitted 

 of a very easy solution, on account o^ periodical motion appear- 

 ing to them as the great means employed by nature for counter- 

 acting the power of gravity, and for maintaining the sun and i\ip 



