34^ Optical Fhicnomemn hy MtoTi'Vight 



hood of the Unicorn : in other places it was quite uniform. 

 The elliptical ring towards the ea(t exhibited a very white and 

 thicker part, which became deranged, and no longer coincided 

 with the ellipfe the nearer the phaenoinennn approached to 

 it? end. This happened a ftw min,utes paft eleven o'clock, 

 after both the rings had loft their colour, and when the moon 

 began to be furrounded by a yellow nimbus. At twenty mi- 

 nutes paft eleven both the circle and ellipfe had difappeared ; 

 but. the nimbus around the moon had fo increafed, that, ac- 

 cording to the eye, it was equal to fix diameters of the moon, 

 or about three degrees. The vapours in the atmofphere were 

 at this time no longer diftributed in an uniform manner, but 

 thrown together in malTes of different dcnfities, which formed 

 regular clouds, and in which fome motion was obferved. Nei- 

 ther fnow nor rain, however, followed, but the weather as well 

 as the temperature of the atmofphere continued the fame. 

 About eleven o'clock the following evening a little cold rain 

 fell ; but the drops were exceedingly fine, and it did not lang 

 continue. 



Having finiflied the defcription of this phaenomenon, it 

 might naturally be expefted that I fliould give fome explana- 

 tion of the caufos which produced it; but I have not fuffi- 

 dent confidence in my own abilities to undertake fo difficult 

 a tafk. As far as can be deduced from the principles of 

 optics and the dottrine of light, it may be afcribed to fome 

 infulated chnid' of different ihickncfs and denfity, or to fe- 

 vcral ftrata of clouds lying near and above each other. The 

 pha?non"ienon of the parafelena, where both rings apparently 

 interfered each other, gives us reafon to conjefture that they 

 aftually cut each other; and that therefore we may admit 

 S3 the caufe the firfl cafe, that is to fa}-, one fingle ftratum of 

 clouds of unequal thicknefs and denfity. It is not improbable 

 that, in regard to the elliptical ring, the cafe was the fame as 

 with the lenticular elevations in common window glafs, 

 which diftort objefts, extend them in length, and give to 

 round things an elliptical form. But, in my opinion, it is 

 niore difficult to explain whv the larger ring was perfe6lly 

 circular, and appeared fo eccentric; why the image of the 

 moon lav at the end of the radius in the periphery. It is 

 verv probable, as has been alreadv remarked by various ob- 

 fervers, that during this phaenomenon there were in the thick 

 Vapours of the atmofphere fevcral hollow cones or funnels 

 which, bordcrinc on the hafis of the image, formed feveral 

 fines; for the latter occafioned, in the places of interfecftion, 

 an appearance of the prifmatic colours. Should this con- 

 jecture be agreeable to truth, the higher geoructry, and par- 

 5 licularly 



