J 811.1 T't'ue Cause of a Comet s TaiL 331 
spasms, which sometimes lasted several 
hours, I gave it as my o|)inion tlint ul¬ 
ceration of tlie kidneys had taken place, 
and would some time be the cause of 
her death, having no conception of so 
large a stone being formed in the in¬ 
testines. Wm. Simmons. 
N. B. The above stone is in my possession, 
■which I intend keeping for the inspection of 
the curious. 
Thame^ Sept, 9, 1811. 
To the Editor of the Monthly Magazine, 
SIR, 
MONO astronomical wonders, the 
Tail of the Comet has always dis¬ 
concerted the conjectures of system- 
mongers; and on this phenomenon we 
have had more hypotheses, than on any 
other tojjicof philosophical investigation. 
If we consult those midw'ives of learn¬ 
ing, the Cyclopedistsj we shall pretty 
uniformly find that the tail of a comet 
has been considered as a collection of 
valours rarefied by the comet^^ approach 
to the sun, and serving as a train to the 
nucleus of the comet. This, however, 
must be a vapour of the brain; for it in 
no degree accords ^vith the phenomenon, 
the tail going before or behind, or to the 
right or left of the nucleus, indifferently; 
and forming at successive times every de¬ 
gree of variation from the course of the 
comet. 
In truth, the direction of the tail 
obeys but one law, and that is to spread 
in a direct line from the Sun, so that the 
nucleus and its coma are constantly in 
the real line drawn from tlie centre of 
the tail to the centre of the sun. Does 
not ibis law prove then, that the comet’s 
tail is nothing more than a peculiar phe¬ 
nomenon of the solar rays ? Does it not 
prove that the tail is a combined effect 
of the solar rays, and of some economy or 
power of adaptation in-the comet itself? 
Even in looking at the comet after sun¬ 
set, with the associations wliich attend 
the phenomena of evening as the solar 
light leaves elevated terrestrial objects, 
are we not insensibly led to consider the 
luminous tail as an emanation of solar 
light? In a word, has it not all the sen¬ 
sible appearance or mere solar rays, as 
viewed with the naked eye and with a 
telescope ? 
How then are solar rays brought into 
that situation? Let us not puzzle our¬ 
selves by hard names, but apply to the 
vast our ordinary perceptions on minute 
objects. We see the atmosphere of the 
jjucleus with the naked eycj as well as 
tvitlj a telescope. It is peculiar to 
metary bodies—-we see nothing like it in 
the planets: hence then we have two 
features of peculiarity, the direction of 
the tail from the sun, and an enlarged 
atmosphere of a peculiar character, by 
which to account for a peculiar accom¬ 
panying phenomenon. Are they sufficient 
to explain it? Perfectly so. Suppose a 
globe of water, with an opaque ball in its 
centre—in other words, the pellucid at¬ 
mosphere of a comet and its nucleus— 
suppose them placed in the sun-shine— 
the situation of a comet at all times—is 
it not then evident the globe of water, 
with its opaque hall, would by the re- 
frttetion and reflection of rays of light, 
exhibit all the phenomena of a cornet’s 
tail, under all the circumstances and 
variations of tiuit tail r* By tlie ordi¬ 
nary laws of refraction, the tad would 
be lengthened as it approached the 
sun, and would shorten as it receded* 
which we know accords with the pheno¬ 
mena. 
The tail of a cornet is therefore a 
grand optical exhibition of the pheno¬ 
menon of light. As the solar rays pass 
in their ordinary course through space, 
they exhibit no peculiar xippearances 
but wiien they impinge on the atmos¬ 
phere of a planetary body, and undergo 
decompositions, refractions, and reflec¬ 
tions; tlien they exhibit their general, 
visual phenomena, wheth.er it be as con¬ 
densed in the sliape of a comet’s tail, or 
in giving luminosity to the figure of a 
planet. As the spherical refracting me¬ 
dium approaches the fountain of light,, 
the foci of convergency of course are 
extended, and the quantity of light is 
increased; and then is the comet’s tail 
of the largest dimensions, and the most 
luminous.f As it recedes from the 
—^--- f ■■ I . ■ » ■ I I - — 
* The character of the cometary atmo¬ 
sphere, anH fluid surface, accords no doubt, on 
my recently published Hypothesis, with the 
powers of centrifugal lorce required to prevent 
j's fulling into the sun, in its perihelion. 
Indeed, the phenomena of the tail, created 
by that required peculiarity of atmosphere, 
serves aj a further proof of my notion, that 
centrifugal forces are created by the action of 
the fluid parts of planetary oodles. 
L The length of the tail am the distance 
from the sun being ascertained, we might 
thence deduce the refrangible power of the 
comet’s atmosphere, and also its sphericity or 
diameter. The principle wliich I have ad¬ 
vanced is indeed capable ol being extensively 
ajiplied in calculating distances. 
fountaia 
