[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.
Derham was a Church of England clergyman and a natural philosopher, interested in nature, mathematics, and philosophy. He frequently requested medical advice from Sloane, and likely served as a physician to his family and parishioners (Marja Smolenaars, “Derham, William (1657-1735)”, Oxford Dictionary of National Biography, Oxford University Press, 2004 [http://www.oxforddnb.com/view/article/7528, accessed 7 June 2011]).
