SIS TORT of the SdCIETT. 7 



An Account of an Aurora Borealis, obferved in day-light at 1799- 



Aberfoyle in Perthfliire, on the loth February 1799, by Pa- An mlr.to. 

 TRICK Graham, D. D. minifter of Aberfoyle, was communi- b"day4ighr 

 cated by the Reverend Dr Finlayson. r 



" On the loth of February 1799, about half-an-hour pafi: 3 

 o'clock P. M., the fun being then a full hour above the horizon, 

 and fhining with an obfcure luftre through a leaden-coloured 

 atmofphere, I obferved," fays Dr Graham, " the rare pheno- 

 menon of an aurora borealis by day-light. The weather, for 

 feveral days before, had been intenfely cold ; and during the 

 two preceding days, mvich inow had fallen. On this day a thaw 

 had come on, and the temperature of the air was mild. The 

 general afped: of the flcy was ferene. Some dark clouds hung 

 on the horizon between S. \V. and W. 1 was intenfely obfer- 

 ving a large halo about the fun, of about 20 degrees in femi- 

 diameter : It exhibited the prifmatic colours, though obfcurely, 

 except in one quarter, where it coincided with the fldrt of a dark 

 cloud on the hotizon, almoft diredlly weft. In that portion of 

 the halo, the colours of the iris were very diftiniflly exliibited. 



Whilst I was attending to this appearance, the whole vifible 

 hemifphere of the heavens became covered with a light palifh 

 vapour, as I at firft imagined it to be. It was difpofed in lon- 

 gitudinal ftreaks, extending from the weft, by the zenith, and 

 all along the Iky towards the eaft. On examining this appear- 

 ance more narrowly, I found it to be a true aurora borealis, 

 with all the characters which diftinguilh that meteor when feen 

 by night, excepting that it was now entirely pale and colourlefs. 

 The ftream of eledric matter iffued very perceptibly from the 

 cloud in the weft, on the Ikirts of which the halo exhibited the 

 prifmatic colours ; thence difFufing themfelves, the rays conver- 

 ged towards the zenith, and diverged again towards every quarter 

 of the horizon ; and the corrufcations were equally inftanta- 

 neous, and as diftindly perceptible as they are by night. 



This 



