Page:The story of the comets.djvu/194

"The head of the comet presented the great peculiarity of having two eccentric envelopes in addition to the ordinary bright envelope immediately surrounding the nucleus. The first envelope was a bright and sharply defined semi-circle surrounding the nucleus: the two eccentric envelopes were nearly as bright, and also very sharply defined, also semi-circular, having their centres placed (about) on the edge of the first envelope, and

Fig. 69.

COGGIA'S COMET OF 1874.

Skeleton outline on July 13. (Brodie.)

a,	g,	a.	Undefined outline of nebulous head.
b,	c,	b.	Fairly defined outline of second envelope.
	d,	d.	Sharply defined outline of first envelope, semi-circular, and very bright.
	e,	e.	Very sharply defined clear dark space between bifurcation of tail, free from nebulosity.
	f,	f.	Singular eccentric envelopes, sharply defined, fading away at and into b b. The centres of those envelopes were at a.
	g,	c.	Between these two points several envelopes concentric with d d were traceable.

intersecting each other. The second centrical envelope just embraced both these eccentric envelopes, and was about half the width of the nebulous head of the comet. Between this second envelope and the ill-defined outline of the head (that is, between c and g) there were faintly marked outlines of other concentric envelopes. The nucleus, which, according to Hind, was 4000 miles in diameter, appeared to be somewhat flattened on