Royal Society. 55 



siderably bright white cloud, thirty degrees in length, and about a 

 degree and a quarter, or a degree and a half in breadth in the mid- 

 dle of its length ; its brightness nearly uniform, except towards the 

 ends, where it faded gradually, so that to define its exact termination 

 at either end was difficult. However, by the best judgement I could 

 form, it might be considered as terminating, to the eastward or fol- 

 lowing side, at, or a very little beyond, the stars t, k, X Leporis, which 

 stars (being of the fifth, or at most 5*4 magnitude) were pretty con- 

 spicuously visible ; from which circumstance the degree of bright- 

 ness of the ground of the sky in that region may be well estimated.. 

 Between these stars and fx Leporis, the luminous band then com- 

 menced, involving neither of them, but more nearly contiguous to k 

 and \ than to /i. From thence its course was towards rr Eridani, which 

 star must have been covered by it, and was not seen ; this judgement 

 of its direction having been formed by noticing that it passed clearly 

 above y Eridani, and as clearly below and parallel to the direction 

 of c, e Eridani, which two stars being dimmed by the vapours of 

 the horizon and the twilight, were so little conspicuous as perfectly 

 to account for ir not having been noticed. At the point of its pass- 

 age between y and 5 it was still considerably bright, and as it ter- 

 minated with somewhat more abruptness at a point beyond e (then 

 about 1 2° high) than at its upper extremity, I am rather disposed 

 to consider this end as somewhat curtailed by the vapours. Making 

 no allowance, however, for this, and estimating its visible termina- 

 tion at a point on a celestial globe nearly opposite £ Eridani (which 

 star however was not noticed at the time), the length above assigned 

 to the luminous band (30°) has been concluded by measurement 

 on the globe. 



I am thus particular in describing the course, situation and di- 

 mensions of the band, not only as terms of comparison with other 

 observations of it, should any have been made, but for another rea- 

 son, in which consists the peculiarity of the phenomenon, and which 

 is my sole motive for making this communication. The above situ- 

 ation and course, relatively to those stars, remained perfectly unal- 

 tered the whole time it remained visible at all, which it did for up- 

 wards of an. hour from the time I first saw it, accompanying the stars 

 in their diurnal motion, until the preceding end at length was extin- 

 guished in the horizon vapours with the stars adjacent, and until 

 the light of the rising moon dimmed and at length effaced the rest, 

 though I apprehend its intrinsic lustre to have been in progress of 

 diminution during the last quarter of an hour or twenty minutes. 



I should not forget to mention, that neither in the north-west, nor 

 elsewhere, were any streamers or other appearances of Aurora Borealis 

 perceptible during any part of the evening. The only other luminous 

 appearance, the milky way excepted, was that of the zodiacal light, 

 which I have seldom seen to greater advantage in this climate, and 

 which extended high enough to involve the Pleiades, then about 

 55° from the sun. 



I have said that the general aspect of the phenomenon was that 

 of a bright white cloud. In fact, my first impression was that such 



