202 Comet II. 1862. 



by a darker interior space, much lighter, however, than the 

 sky ; the separation commencing some way behind the head, 

 and becoming more distinct in its progress. The right inverted 

 branch is much the longer, narrower, and better defined, reach- 

 ing certainly at least 3^°, and possibly considerably further ; it 

 seems concave to the right, not so perceptibly as before in any 

 one field, but decidedly in the whole length (as to this, how- 

 ever, I have subsequently become uncertain, from noting the 

 deceptive effect of the motion of an equatorial mounting, placed 

 very far out of the meridian) . The left branch of the tail is 

 short, broad, comparatively faint, very ill-defined, and not 

 extending more than lf° from the nucleus. As far as its light 

 is tolerably distinct, it would seem, with the intervening 

 darker space, to complete the perspective of a hollow structure, 

 but beyond its termination, the other branch streams onwards 

 so distinctly defined on both sides, and insulated on the dark 

 sky, as to preclude any other supposition than that of separate 

 existence ; it is here 7' or 8' broad, and does not expand at all 

 in its progress; the definition of its edges is remarkable. 

 The coma is generally less luminous on the side turned from 

 the sun, but there is no dark interval for a considerable 

 distance behind the nucleus, and the origin of the tail is con- 

 fused ; the right branch seems to point to the nucleus and the 

 brighter area to the left of it, as far as the set-off; the left 

 branch appears to be a continuation of the left side of the 

 coma, exterior to this boundary; so that the origin of the 

 central darkness 'might possibly be referred to the dark channel 

 supposed to adjoin this set-off, could its existence be verified ; 

 this, however, is doubtful, as the region behind the head is filled 

 with confused haze. The passage of the nucleus near several 

 small stars is very striking. Micrometrical measures of distance 

 cannot be taken, in the absence of an illuminating apparatus ; 

 and an attempt at estimation is subsequently found in error ; 

 but fig. 2 gives something of the general effect. 



August 23. Very clear night. Another great change : the 

 nucleus has become strikingly more brilliant, but not stellar, 

 being undistinguishable from the commencement of a luminous 

 arc, shorter, narrower at the further end, and less curved than 

 the " feather " of last night, but of so sharp and vivid a light, 

 especially towards the nucleus, as to bear distinctly every 

 power even up to 460. With a beautiful microscopic eye-piece 

 by Powell and Leland, power somewhere about 300, the 

 nucleus could just, though barely, be distinguished at its 

 end ; it is very minute, and cannot exceed 1". The wider 

 extremity of the arc is less abruptly terminated than that of 

 the feather ; its direction is obviously quite changed, and either 

 the feather has retrograded through a considerable space^ or 



