late Professor of Practical Astronomy in Glasgow. 293 



For, one day when observing a spot of considerable size near the 

 sun's limb, he actually beheld this appearance of the dusky zone 

 .which belongs to the nucleus, finding it almost wholly deficient 

 on that side which respected the centre of the disk ; and this, too, 

 when the distance of the spot from the limb corresponded very 

 nearly with that which Dr WILSON found to be so constant in 

 his observations. Mr FLAMSTEAD was then, indeed, viewing his 

 spot in peculiar circumstances, and the most favourable of all to 

 perfect vision of the sun, as, by the intervention of a mist, he was 

 enabled to use his telescope without the help of tinged glass put 

 before his eye. The following is his account of this remarkable 

 observation, in which, by the word macula, Mr FLAMSTEAD evi- 

 dently 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 turn lon- 

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

 dorem munire soleo) maculum contemplatus sum : distincta valde 

 videbatur, ejusque figuree quae in schemate adpingitur : ' Nu- 

 ' becula ipsi circumducta elliptica omnino ; sed, quod valde mi- 

 ' ratus sum, admodum dilatata a parte limbum respiciente ; ab 

 ' altera vero versus centrum, macuke fere cohserere videbatur.' 



" Observavi dein macuke a limbo proximo distantium 1' 13"." 

 Hist. Cosiest. FLAMSTEEDII, vol. 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 be- 

 ing an excavation or depression on the luminous matter of the 



