Letter 1127

[fol. 334] Sr Upminster Apr 7 1707 The Afternoon of Thursday Apr: 3 last I devoted in some measure to the service of the R. Society, to take Angles in order to finish my Observations about Sounds. And as I was returning hence, I perceived in the Western past of the Heavens, about a quarter of an hour after Sun- set, a long slender Pyramidal Appearance, perpendi- cular to the Horizon. The Base of this Pyramid I judged to be doubtless the Sun (then below the Horizon.) Its Apex reached 15 or 20gr above the Horizon. Wh It was through out of a rusty red colour; & when I first saw it, pretty vivid & strong; but the top-part fainter much than the bottom, nearer the Horizon. The At what time this Appea rance began, whether at, or how soon after Sun-set, I cannot say, being at that time in a ffriends house. But about a quarter of an hour after Sun-set, as soon as I was gotten abroad, I perceived it, I had for some time a fair prospect of it, the Horizon being pretty free & open where I then was. But after a while, it grew by de- grees weaker & weaker, so yt in about a quarter of an hour after I first saw it, the top-part (a.b.d. in the inclosed Figure 1) was scarce visible But the lower part remained vivid much longer, but yet grew by degrees Shorter & Shorter. I saw the Remaines of the lower half (b.d.e.f) a full hour after Sun-set; and should perhaps have seen it longer, had the Horizon been open. But it was often in my walk pent up wth trees, wch not only obstructed my sight of the end of this unusual Appearance, but also hindered me from an exquisite obser- vation of all the particulars yt might probably occur. The whole Atmosphere seemed hazy, & full of Vapours, especially towards the Sun-set. The Moon & Stars were yt evening bearded at yt time, & succeeded wth an Halo about ye Moon afterwards. Which disposition of the Air was pro- bably the cause of the Phenomenon. But the Pyramis was undoubtedly imprinted upon the far distant Vapours of the Atmosphere: it being manifestly farther off, or lying beyond some small thin Clouds (c.l:c.l.) that intercepted it and in those parts covered & hit it. Although I have the greatest part of my life been ready enough to take notice of such Appearance, yet I do not remem- ber I ever saw any thing like it, except the white pyrami- dal Glade, or wch is not entituled by ye name of the Aurora Borealis. And it being (except in Colour & Length) so like I have thought it worth your cognizance; & if you think of our most illustrations of famous Society also, because it may perchance in some measure conduce to the solution of that odd Phenomenon, the Aurora Borealis I was just going to give you some of my Observations about the migration of Birds this Year, wch make me hope that that subject is within the reach of the R. Society to discover. But being prevented, I have not time just now, but shall reserve it for a more convenient oppor- tunity when I have more leisure. I therefore desire yt what I now send may be an acceptable testimony of my great respects for you, & the Society, & that I am Sr Your much obliged & humble servant Wm Derham I forgot I tell you that I have searched every night since, for this Pyramis Vespertina, but have not seen any such appearance, although the next evening was hazy & likely. I also looked out to see whether the Aurora Borealis would succeed in the room thereof, but discovered no such thing.