45 OhfervailoTis on the ^poh of (be Sun^ 



quantity. By obferving the fun, we perceive not only the 

 luminous matter, but the light rcflefted, in a lively manner, 

 from the fun's body ; and at fuch a diftance they cannot 

 be diftinguiflied from each other. Through a deception of 

 our fenfcs, we often take tlie effeft for the caufe, and feek 

 for the' objeft in the light, and then again for the light in 

 the objecl. 



But as the atmofpherc, greatly expanded at the equator, 

 mull fink down fomewhere from well known caufes, the lu- 

 minous matter flies off" on all fides towards the lower parts, 

 and illuminates the parts it left, no longer from above, but 

 laterallv. Here we difcover the folar faculoe ; and if in thofe 

 parts there be inequalities, there arife then half (liadows, 

 which arc almolt loll in the tint of the ground. If the ob- 

 ferver fails in his judgment of the angle of inflexion, he fees 

 only a mixture of faint fpots, and no landfcapes. 



It will now be eafier to explain the proper fpots in the fun, 

 as they are called. They are parts of the fun lying under 

 full (hadows, which mud naturally arife when the illumi- 

 nating fluid draws itfcU fo far back from the horizon of that 

 neighbourhood, that no more rays can reach its centre. The 

 contralt with the refl: of the dazzling difk of the fun in- 

 creafes their blacknefs, and gives them the appearance of a 

 burnt coal, or cinder. We Ihall be readily convinced that 

 fome parts of the fun's furface may lie in a full fliadow, when 

 we refleft on the great fize of thefe fpots, and confider tlie 

 height of the luminous fluid to be fmall, or equal to about 

 the diftance of our highcft clouds from the earth. It cannot 

 be higher, elfe no perceptible half fliadows would be occa- 

 fioned, bccaufe the fliadows of bodies become fmaller in pro- 

 portion to the height of the illuminating point. The irregu- 

 larity of the fpots arifcs partly from the different fituations of 

 the luminous matter, and partly alfo from the inequality of 

 the bottom. That remarkable vapour by which thev are 

 furroundcd is occafioned by a kind of crepufculum, by which 

 the fide light is conveyed to the moft diflant part from the 

 centre of the fliadow. As the luminous matter now appears 

 to be more fparingly divided in the folar atmofphere, a place 

 may be totally deprived of light by its retiring: but near 

 the boundary of the light it is direited towards ihe bottom, 

 though fomewhat weakened by the refra6lion and refledlion 

 of the rays, as is the cafe in our morning and evening crc- 

 pufcula ; and the fpots by thefe means obtain their conical 

 form. If we confider this vapour more attentively, the be- 

 fore-mentioned landfcapes can be clearly diftinguiflied ac- 

 cording to the above method 3 and if the full" fhadows have 



confiderable 



