A

S T R O N Q M V.

is 46 . u, -

’ v '°Hv et > s y( in g thus shewn the several Affections of a

219

>»

CSn

Potion,

Plate

I shall conclude with a Word or two LXIII,

j ^ftiticf 1 t0 t ^ le ‘ r Tails. The Atmosphere of Comets Fig, 2.* iti °f a very fine Vapour, will, when the Comet* ^Pbdioti, be nearly spherical, and its Density■ e at e ,’ ^.s the Comet approaches the Sun, the Sun’3ftOsu,” ers the Atmosphere, and rarifies it by Degrees,

^ l he same Time the finest Part to raise from the'V e , hse the Flame from a Candle, towards the Parts

?»d ^ the

self ^ref

Sun ; and as the Comet comes nearer

ps

the Sun, this Fume will rife and extend it-

l^^er and greater Lengths, and make what is

\i"‘"'Ttiil of the Comet; so that when they are

jd'd 'I' a ij' r * t ^ a Telescope, the Nucleus , Atmosphere,

fte<j j °f a Comet appear much like what is repre-

s < ? . "^Figure. -■■■_

i^ioh length of the Tail is thus found by Ob-

j 5rt h A Let S be the Sun, C the Comet, T the

t the Comet’s Tail; draw T S, T C, S C, Fig. 3.

p't.t § f p° Uc hing the End of the Tail, and meeting the

hNet l P ro duced in E. The Place of the Sun andlo; bi

p e ‘ n g known, the Angle T C E is known (for

^STC + CST) A ' "

. * ^ lo 1» m a. — __ f"

is' 0 ' ^

ilWto,'"'* is known from Observation

M .

if hw*- Therefore in the Triangle 1 C e, having

[N t u^ n gLs TC« and C T r, and the Sidefh e r 'he "ph

Also the Angle of Devi-whence TCsoreover the Angle T C r is known also by

TC,

leory) we can find the Side C r, which isH T*Sth of she Tail."' And thus'they have been[j 48 , p\° e 40 , 60, and 80'Millions of Miles.jj^Us e - ,f avv S e cutting the Comet’s Orbit in d ; thenjj C r es 0 [ . Whole Motion of'a Particle from C to e may4 ^ into two Motions C d and e d, ’tis plain,M ls that directly averse to the Sun, the Comett,A tes„ a y e poslfess’d the Point d when the Particle at e' 0| n the Nucleus., if the Motion had been every■tip-v Direction of Sr, as the Line Sr kept" 0ni S r to S E. ‘ ' ’ " ' °

.j hut the Particles

oblique Direction C r, therefore parallel to

. 49. p or..

P^in this'is'not the Cafe,

*ill

cutting the Orbit in1 le compound Motion C r,

5 ■ " ' ,

D, and join D r ;arising from theprogressive