256 
fraiion into feven different colours; 
others have contended that it is divifible 
into three only ; now Dr. Wollafton con- 
reverts the opinions of both parties, and 
declares that four, and four only, primary 
divifions of the prifmatic {peétrum can be 
difcovered ; and he conceives that he has 
afcertained this point with a degree of dil- 
tinctnefs that has not been defcribed ner ob- 
terved before. ** If (fayshe) a beam of day- 
light be 2dmitted into a dark rcom bya ere- 
vice #4, of an inch broad, and received by 
the eye at the diftance of ten or twelve feet, 
through a prifm of flint glafs, held near 
the eye, the beam is feparated into the 
four following colours only, red, yellow- 
wh-green, blue, violet.”” And the pro- 
portions of the {paces occupied by them 
will be as 16, 23, 365 25. 
By the fame gentleman we. have ano- 
ther paper ‘ On the oblique refraction of 
Iceland Cryftal.” The experiments de- 
feribed in this communication go to efta- 
blih the theory long fince laid down by 
Huygens, in his Traité de la Lumiére. 
“© The obfervationsthat I have made on 
this fubfiance (fays Dr. Wollafton) ac 
cord throughout with this hypothefis of 
Huygens ; the meafures that I have taken, 
correfpond more nearly than could well 
happen to a falfe theory, and are more 
to be depended on, as all my experi- 
ments, excepting the laft, were made prior 
to my acquaintance with the theory, and 
their agreement was deduced by fubfe- 
quent computation.” 
Dr. Young’s account of fome cafes of 
the preduction of colours not hitherto de- 
icribed will be read with intereft. His 
method of accounting for atmofpherical 
halos, we fhall defcribe at large. ““ When 
a number of fibres of the fame kind, for 
inftance an uniform lock of wool is held 
near the eye, we fee an appearance of 
halos furrounding a diftant candle; but 
their brilliancy, and even their exiftence,* 
depends on the uniformity of the dimen- 
fions of the fibres, and they are larger as 
the fibres are fmaller. It is obvious that 
they are the immediate confequences of 
the coincidence of a number of fringes 
of the fame fize; which, as the fibres are 
zrranged in all imaginable directions, 
mutt neceffarily furround the Juminous ob- 
ject at equal diftances on all fides, and 
conftitute circular fringes. 
* The fame appearance has been frequently 
obferved by a perfon, (before whom a candle 
flood) inthe aét of falling.afleep; in which 
cafe, the hairs in the eye-lafhes evidently 
act asthe fibres of wool. Epitor, 
Proceedings of Learned Socteties. 
[April 1, 
“There can be little doubt that the co- 
loured atmofpherical halos are of the fame 
kind ; their appearance muft depend on, 
the exiftence of a number of particles of - 
water, of equal dimenfions, and in a pro- 
per pofition with refpe&t to the luminary 
and the eyes Ass there is no natural limit 
to the magnitude of the fpherules of wa- 
ter, we may expect thefe halos to vary 
without limit in their diameters; and it 
has been obferved not only that their di- 
menfions are various, but that they fre- 
quently change during the time of ob- 
fervation.” 
AMERICAN PHILOSOPHICAL 
SOCIETY. 
NATURAL HISTORY. 
R. BARTON, in his Account of 
the Poifonous and Injurious Hosey 
of North America, obferves that honey 
muft always partake in a greater or leffer 
degree of the general properties of the fiow- 
ers trom which it is obtained. ‘The fymp- 
toms and effects produced by this deleterious 
honey are, dimuefS of fight, vertigo, and 
delirium : thefe are fucceeded by pains in 
the inteftines, convulfions, profufe per- 
fpirations, foaming at the mouth, vo- 
miting, and purging. In a few inftances, 
death is the confequence, though this but 
rarely happens, as the vomiting and per- 
fpiration are ulually favourable to the te- 
covery of the fufferer. Dr. Barton next 
defcribes the feveral plants and vegeta- 
bles from which the bees extraét this 
wild and deleterious honey; but he fup- 
pofes there are many others, of which he 
is ignorant; and feems to conclude that 
every flower that is poifonous to mans 
and is capable of affording honey, may 
produce a fort that will be injurious to 
him, and hence he contefls the pofition of 
our poet . 
In the nice bee, what fenfe fo fubtly true 
From pois’nous herbs extraéts the healing 
dew, Essay on Man. 
He next fhews that deleterious honey 
was known to the antients; and, among 
other faéts, quotes the circumftance re- — 
lated by Xenophon, of his own army, ” 
when they had arrived on the coaft of the - 
Euxine Sea. He alfo refers to Virgil, 
who, in his fourth book of the Georgics, 
cautions his readers againft fuffeting a 
yew-tree from growing near the bee- 
hives— 
Neu proprius te¢tis taxum fine. 
And in his 9th eclogue, the fame poet 
fpeaks 
