168 W. A. Norton—Coggia’s Comet. 
Frying Mer Aap 
showed that the ‘columnar structure” of the tail, signalized 
by Prof. Bond, was attributable to considerable variations, at 
short intervals, in the quantity of matter detached from the 
head of thecomet ; while the limits of variation of the effect- 
between the limits, repulsion=1-415 A and attraction=0°786 A. 
orce of Cosmical Repulsion.—Several hypotheses have been 
propounded with regard to the nature and origin of this force. 
But none of them appear to be free from serious objections. 
Several years since (1861) I suggested the hypothesis that the 
solar repulsion might consist in the repulsive action of free 
statical electricity. We have abundant evidence of electric 
excitation both at the surface of the sun and in the cometa 
sun as an electro-magnet + on the gaseous molecules of the comet. 
- - F. Zollner, in two elaborate papers published in the Astronomische 
Nachrichten, No. 2057-2060 and No. 2082-2086, has endeavored to remove the 
force of the several objections urged by Dr. Zenker to the electric theory of the 
lar repulsion, and gang the adequacy of this theory. Dr. Zenker has pub- 
our =m ‘ 
y A discus- 
sion, it does not appear that the above-mentioned objection has been set aside. It 
must be admitted, I think, that at present the tric theory rests under a 
of doubt. As for Dr. Zenker’s own reaction theory, to mention no other objec- 
tions, it is certainly wholly inapplicable to the case of a co ming as near the 
sun as did the comets of 1843 and 1860; and it obviously affords no explanation 
ee oe ure of ia’s comet. 
e term electro-magnet is meant a magnet which derives its magnetic 
condition from the continued operation of some external cause. ae 
